single ion imaging with a microfabricated optic · one real-world application of atomic vapour...

512 Th 103 Precision Measurements...

Single Ion Imaging with a Microfabricated OpticE.W. Streed1, B.G. Norton1, A. Jechow1, T.J. Weinhold2, D. Kielpinski1,

1Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Queensland,Australia

2QT Lab, University of Queensland, Brisbane 4072, Queensland, Australia

Trapped ions are a leading technology for implemented quantum computing. Smallscale demonstrations have already been realised and a roadmap exists for scaling tolarger processes1 through an architecture of multiple parallel processing regions imple-mented on a microfabricated trap. A limiting factor in the realisation of large scalequantum computation is the development of a scalable method for efficiently couplinglight out of the trapped ions. Arrays of micro-fabricated phase Fresnel lenses (PFLs) area promising solution 2 to this problem as they are easily scalable and have high numeri-cal aperture for capturing a large fraction an ion’s solid angle. Figure 1a. indicates howa PFL array could be combined with a microfabricated trapped ion Quantum CCD pro-cessor architecture for parallel readout. The diffraction limited performance2 of PFLswith large numerical apertures also makes them suitable for obtaining large coherentcoupling between an individual ion and a single optical mode, crucial to realising largescale quantum networks through remote entangling protocols.

To demonstrate the feasibility of this approach we have integrated together an RFneedle trap with an in vacuum, large aperture PFL (Fig 1b) which captures light from12% of the total solid angle (NA=0.64). Single 174Yb+ ions were loaded into theRF quadrupole potential formed between the needles through isotope selective photo-ionisation. The emitted ion fluoresce from laser cooling was subsequently imaged withthe PFL. We have observed a depth of field of 30µm and a field of view in excess of100µm for ions with a spatial width (1/e2) of 4.4µm, limited by the ions motion. Cor-recting for a reduction in the ions maximum brightness due to this motion we observedan overall collection efficiency of 4.2± 1.5% and a signal to noise ratio of 23± 4. Thisreadout performance is sufficient for large scale quantum processing2.

Yb+

b.a.

Figure 1: a. Phase fresnel lens array for large scale quantum computing1. b. Experi-mental apparatus configuration.

1D. Kielpinski, C. Monroe, and D. Wineland Nature 417, 709 (2002).2E. W. Streed, B. G. Norton, J. J. Chapman and D. Kielpinski (2009) Quantum Information and Computa-

tion. 9 pp0203-0214

Precision Measurements... Th 104 513

Ultra-Sensitive Magnetometry using Atoms in FibresD. Stuart1, C. Ironside2, C. Perrella1, A.N. Luiten1

1School of Physics, University of Western Australia, Nedlands, Western Australia,Australia

2Department of Electronics and Electrical Engineering, University of Glasgow,Scotland, United Kingdom

One real-world application of atomic vapour spectroscopy is the precision measurementof magnetic fields. As one example, SERF atomic magnetometers have been realisedwith sensitivities of 0.5 fT Hz−1/2, surpassing that of SQUID-based magnetometers1.These ultra-sensitive magnetometers are capable of measuring biological magnetismfrom the heart (magnetocardiography) and brain (magnetoencephalography), however,they can only be operated at very low magnetic fields. For high field applications, weaim to build an all-fibre atomic magnetometer using the phenomenon of coherent popu-lation trapping.

Coherent population trapping occurs when atoms (of Rubidium, for example) areexposed to a multimode optical field containing two frequency components separatedby the ground state hyperfine splitting. When this happens, the atoms can be opticallypumped into a “dark state”: a coherent superposition of the two ground states whichdoesn’t interact with the optical field. The narrow “dark state” resonance has applica-tions in miniaturised atomic frequency standards2, quantum memory3, and magnetome-try4. The two most common ways of generating the two-component optical field are bymodulating a laser to generate sidebands, or by phase-locking two lasers. Preliminarymeasurements have been made by modulating a diode laser and performing spectroscopyon a magnetically shielded Rubidium-85 vapour cell. We have succeeded in measuringthe CPT resonance and have used this to see a magnetic field.

In the future, we intend to use a specially fabricated self-modulating diode laserincorporating a resonant tunnelling diode (RTD): the fastest known electronic devices(demonstrated operation at 831 GHz5). The RTD has intrinsic electronic gain and cangenerate self-sustaining modulation, eliminating the need for a microwave oscillator. Inaddition, we aim to use Rubidium vapour loaded in a hollow-core photonic crystal fibreto replace the glass vapour cell. This approach has the advantage of combining the celland laser in a self-contained all-fibre system that avoids any magnetic material near thecompact and robust sensor.

1I. Kominis, T. Kornack, J. Allred and M. Romalis, A subfemtotesla multichannel atomic magnetometer,Nature 422, 596-599 (2003)

2S. Knappe, V. Shah, P. Schwindt, L. Holberg, J. Kitching, A microfabricated atomic clock, Appl. Phys.Lett. 85, 1460 (2004)

3M. Lukin, Colloquium: Trapping and manipulating photon states in atomic ensembles, Rev. Mod. Phys.75, 457472 (2003)

4D. Budker and M. Romalis, Optical magnetometry, Nature Physics 3, 227 - 234 (2007)5J. Figueiredo, B. Romeira, T. Slight and C Ironside, Resonant Tunnelling Optoelectronic Circuits, in

Advances in Optical and Photonic Devices (ed. Ki Young Kim), ISBN 978-953-7619-76-3 (2010)


Precision measurements of the Casimir force betweenmetallic and semiconducting plates

A.O. Sushkov1, W.J. Kim2, D.A.R. Dalvit3, S.K. Lamoreaux1

1Yale University, Department of Physics, P.O. Box 208120, New Haven, CT 06520,USA

2Seattle University, Department of Physics, 901 12th Avenue, Seattle, WA 98122, USA3Theoretical Division, MS B213, Los Alamos National Laboratory, Los Alamos, New

Mexico 87545, USA

Casimir effect describes short-range quantum forces between a pair of macroscopic ob-jects. The Casimir force is among the dominant forces affecting MEMS and NEMS,causing stiction and dissipation, and the possibility to control this force can have enor-mous technological benefits. Measurements of the short-range attractive force betweena pair of plates separated by 0.7 µm to 100 µm have been performed using a torsion bal-ance. The force between crystalline germanium plates is found to contain contributionsfrom both the Casimir force and a residual electrostatic force, generated by surface patchpotentials. We have developed a model, taking into account long-range variations in thecontact potential across the plate surfaces, which reproduces our experimental observa-tions. Improved-precision measurements of the attractive force between plates coveredwith a carefully prepared gold film show that the patch-potential electrostatic force isessentially absent, and the Casimir force can be extracted with improved accuracy.


Techniques to reduce the acceleration sensitivity ofcavity stabilized lasers*

M. J. Thorpe, D. R. Leibrandt, J. C. Bergquist, T. Rosenband

National Institute of Standards and Technology, Boulder, Colorado, USA

We present techniques to reduce the acceleration sensitivity of laser local oscillators(LLO). LLOs with a high fractional frequency stability (∼ 1 × 10−15 or better) playa crucial role in a range of scientific investigations including: optical atomic clocks,gravitational wave detectors, and searches for time-variation of fundamental constants.State-of-the-art LLOs are currently based on lasers that are tightly locked to well isolatedFabry-Perot (FP) cavities with the Pound-Drever-Hall locking technique. All FP cavitydesigns are sensitive to accelerations and it remains a challenge to reach shot noise andthermal noise limited performance.

In response to this problem, we have developed two approaches to reduce the accel-eration sensitivity of FP cavities. The first uses a spherically symmetric cavity spacerto reduce the intrinsic acceleration sensitivity of the cavity length to 10−10 dL/L/g. Thespherical spacer is held rigidly at a ‘magic angle’ that suppresses changes in the cavitylength due to squeezing of the mounting structure. The rigid mounting structure makesthe cavity robust against misalignment in situations where it is bumped or moved. Thesecond approach uses measurements of the accelerations experienced by an FP cavityto cancel the resulting frequency fluctuations in real-time. Measurements from six ac-celerometers positioned around the cavity are input into a field programmable gate array(FPGA) that implements a Wiener filtering algorithm to predict the frequency fluctua-tions. The FPGA also controls the frequency of an acousto-optic modulator positionedbefore the cavity, which cancels the fluctuations in real-time.

*Supported by ONR


Ultrahigh-fidelity quantum gates using smoothcomposite pulses

B.T. Torosov1,2, N.V. Vitanov2

1Department of Physics, Sofia University, James Bourchier 5 blvd, 1164 Sofia, Bulgaria2Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 5209, BP 47870,

F-21078 Dijon, France

Excitation by composite pulses is routinely used in nuclear-magnetic-resonance exper-iments, in order to achieve excitation profiles with prescribed shapes1,2. The methodconsists of applying several consecutive pulses with appropriate relative phases. In suchway one can achieve a robust analog of the traditional resonance pulses. This techniqueis, however, mainly developed for pulses with rectangular temporal shape.

In this work we show that composite pulses with smooth temporal shape can beused to obtain analogues of the π-pulses with arbitrarily flat excitation profile. Thetransition probability can be made robust against variations in the pulse area and/or thedetuning. As the number of pulses increases, the excitation profile becomes increasinglyinsensitive (flat) to small deviations. In order to achieve this, we use the well-knownanalytic solution of the Rosen-Zener model3, which assumes a hyperbolic-secant pulseshape and a constant detuning:

Ω(t) = Ω0sech(t/T ), ∆(t) = ∆0, (1)

where Ω(t) is the Rabi frequency, and Ω0, ∆0 and T are constant parameters. Wecalculate the total propagator by multiplying the phased propagators for each pulse.Then we take the Taylor expansion of the full propagator and nullify the first few termsin the respective series (vs. the pulse area deviation or vs. the detuning). The morecomposite pulses we use, the more terms we are able to nullify, and the more flat theprofile will be.

1M.H. Levitt, Prog. NMR Spectrosc. 18, 61 (1986).2S. Wimperis, J. Magn. Reson. 109, 221 (1994).3N. Rosen and C. Zener, Phys. Rev. 40, 502 (1932).


High Accuracy Spectroscopy of Alkali Metals for theDetermination of the Boltzmann ConstantG. Truong1, D.L. Stuart1, T.M. Stace2, E.F. May3, A.N. Luiten1

1Frequency Standards and Metrology, School of Physics, The University of WesternAustralia, Perth

2Dept. of Physics, The University of Queensland, Brisbane2Centre for Energy, School of Mechanical Engineering, The University of Western

Australia, Perth

The recently developed technique of Doppler-broadened absorption spectroscopy hasbeen shown to be a viable new method for highly accurate determinations of the Boltz-mann constant (kB). In 2009, Djerroud et. al.1 reported a determination with a relativeuncertainty of 3.8 × 10−5, using NH3 at the freezing point of water. A similar exper-iment using CO2 transitions2 has derived a value of kB with a relative uncertainty of1.6× 10−4.

We will report on the progress of an alkali-atom Doppler-spectroscopy effort under-way at the University of Western Australia. Unlike the molecular experiments, stronglyabsorbing alkali metal gases allow us to use compact, low pressure reference cells whichare amenable to high temperature uniformity while avoiding pressure-induced perturba-tions seen in higher pressure regimes. However, these advantages are traded-off againstthe larger homogeneous to inhomogeneous linewidth ratio (∼ 1/100), requiring thenon-linear fitting process (used to extract kB from the inhomogeneous component) beextremely robust. In addition, strong optical pumping effects and unresolved hyper-fine structure in the D2 lines of Rb and Cs complicate the spectrum by perturbingthe Doppler-broadened lineshape, introducing a systematic error that is challenging tomodel.

Using Rb and Cs vapours, we have determined the Boltzmann constant with a rel-ative uncertainty of 4.0 × 10−4. We are currently limited by low signal-to-noise ra-tio (SNR), imposed by the requirement to operate at very low intensities to avoid bothpopulation and lineshape perturbations. To remove this restriction and allow us to usegreater probe powers, thereby improving the SNR, we have developed a detailed model3

with no fitting or phenomenological parameters that accounts for the ballistic motionof open three-level atoms through a probe beam with gaussian spatial profile. We willshow that this model agrees with experiment at the few percent level over four orders-of-magnitude of probe power. The success of this theory will allow spectroscopists todepart from phenomenological models, and will allow us to improve our determinationof the Boltzmann constant in future experiments, by providing a reliable way to extrap-olate high SNR results to the zero-probe-power limit.

1Djerroud et. al.,Comptes Rendus Physique 10 (2009)2Castrillo et. al.,Comptes Rendus Physique 10 (2009)3Stace and Luiten, PRA 81 (2010)


Precision Measurement of the Decay Rates to theGround State for the Helium n=2 Triplet Manifold

S.S. Hodgman, R.G. Dall, L.J. Byron, S.J. Buckman, K.G.H. Baldwin, A.G. Truscott

Research School of Physics and Engineering, Australian National University,Canberra, ACT, Australia

This work represents the first complete measurement of the radiative decay rate to theground state of the n=2 triplet states of helium i.e. the metastable 2 3S1 state and the2 3P manifold. We employ laser cooling and trapping in an ultrahigh vacuum chamberto enable direct measurement of the trap loss rate for decay from the 2 3P1 state tothe ground state. We then use this rate to calibrate the XUV emission decay to theground state for all the remaining transitions. The 2 3P1

1 and 2 3P22 transition rates

are measured for the first time, an upper bound is placed on the 2 3P0 decay rate, andthe 2 3S1 metastable lifetime is determined for only the second time with a five-foldimprovement in accuracy 3. A summary of the ratio of our experimental values to themost recent theoretical determinations 4 is shown in figure 1.

S1 P

2

P1

Figure 1: Ratio of present experimental results to the most current QED theory .

1R. G. Dall, K. G. H. Baldwin, L. J. Byron and A. G. Truscott, Phys. Rev. Lett. 100, 023001 (2008).2S.S. Hodgman, R. G. Dall, K. G. H. Baldwin, and A. G. Truscott, Phys. Rev. A 80, 044501 (2009).3S.S. Hodgman, R. G. Dall, L. J. Byron, K. G. H. Baldwin, S.J. Buckman and A. G. Truscott, Phys. Rev.

Lett. 103, 053002 (2009).4G. Lach and K. Pachucki, Phys. Rev. A 64, 042510 (2001).


Investigation of Highly Sensitive Atomic MagnetometerY.F. Xu1, S.G. Li1, X. Zhou1, X.C. Cao1, A.L. Yang1, X.B. Tong1, Z.Y. Wang1,

Q. Lin1,

1Institute of Optics, Department of Physics, Zhejiang University, Hangzhou , China

Highly sensitive magnetometers capable of measuring magnetic fields below 1 pT areimportant for many applications such as geophysical surveying, space science, medicaldiagnoses etc. For decades, superconducting quantum interference devices (SQUIDs)have been unrivalled as ultrahigh-sensitivity magnetic field detectors, with a sensitivityof 1 fT/Hz1/2.

The atom magnetometer is based on the measurement of Larmor spin precession ofoptically pumped atoms. It has reached and even surpassed1 the sensitivity of SQUIDs.It can also be very compact which is important in magnetic imaging applications. Dueto higher sensitivity and spatial resolution, atomic magnetometers would enable newapplications.

We report a simple and highly sensitive all-optical atomic magnetometer that usesthe advanced technique of single laser beam detection based on the interaction betweenlaser beam and rubidium atoms in magnetic field2. This interaction is dependent on themagnetic field surrounding the Rb atom cell, therefore the magnetic field informationcan be obtained by measuring the changes of the laser power transmitted through the Rbatom cell. A sensitivity of 0.5pT/Hz1/2 has been achieved by analyzing the magneticnoise spectrum, which exceeds that of most traditional magnetometers. This kind ofatomic magnetometer is very compact, has low-power consumption, and has a hightheoretical sensitivity limit, which make it suitable for many applications.

We also analyzed some important factors that may affect the sensitivity of the mag-netometer, such as the temperature of the Rb cell, laser intensity, detuning, polarization,diameter, and the ways to improve the sensitivity of the atomic magnetometer. It isshown that higher sensitivity can be obtained by using laser with larger diameter, higherpolarization, smaller detuning, choosing an optimum temperature and laser intensity.

This work was supported by the National Natural Science Foundation of China(60925022 & 10804097) and the Research Fund for the Doctoral Program of HigherEducation of china (20090101120009).

1I.K. Kominis, T.W. Kornack, J.C. Allred and M.V. Romalis, “A Subfemtotesla Multichannel Atomic Mag-netometer”, Nature 422, 596 (2003).

2S.G. Li, Y.F. Xu, Z.Y. Wang, Y.X. Liu and Q. Lin, “Experimental Investigation on a Highly SensitiveAtomic Magnetometer”, Chin. Phys. Lett. 26, 067805 (2009).


Cold atom gravimeter for onboard applicationsR. CHARRIERE, M. CADORET, N. ZAHZAM, Y. BIDEL, A. BRESSON

ONERA, Departement de Mesures PHysiques, 91 761 Palaiseau, FRANCE

Atom interferometry is now proven to be a very efficient technique to achieve highlysensitive and absolute inertial sensors. As a matter of fact accelerometers such as gyro-scopes 1 or gravimeters 2 based on this technique by using cold atoms have already beendevelopped. However state of the art laser cooling techniques are still too sensitive toenvironmental disturbances to ensure onboard applications with such instruments.We are presently developping a Rb85 cold atom gravimeter based on a compact andreliable laser system operational in onboard conditions. The optical system relies onthe frequency doubling of a telecom fiber bench at 1560 nm 3. The starting point ofthe gravimeter is a vapour loaded MOT of ≈ 108 atoms. The atoms are then releasedand during the fall a sequence of three Raman pulses forms a Mach-Zehnder type in-terferometer. The interferometer’s phase, which depends on the gravity acceleration, isfinally read by means of a fluoresence detection measuring the population of the twoatomic states involved in the raman transitions.Besides last results we obtain on gravity acceleration measure, we will present the de-tails of the experiment setup and particularly the optical part which partly garantees theonboard character of the gravimeter. This laser setup has already been tested success-fully under micro (≈ 0g) and hyper (≈ 2g) gravity inside the CNES ZERO-G Airbusplane in the frame of the ICE (Interferometrie Coherente pour l’Espace) project 4.We are also implementing a new technique for measuring the gravitational accelerationrelying on the use of light pulse atomic interferometry with atoms performing Blochoscillations in a vertical optical lattice 5. This should significatively reduce the fallingdistance of the atoms, which set the height of cold atom gravimeters, without decreasingthe sensitivity of the instrument.

1T. L. Gustavson et al., PRL 78, 2046 (1997)2A. Peters et al., Metrologia 89, 25 (2001)3F. Lienhart et al., Appl. Phys. B 89, 177-180 (2007)4G. Stern et al., EPJD 53, 353-357 (2009)5M. Cadoret et al., PRL 101, 230801 (2008)


A Quantum Degenerate Source for Atom InterferometryM. Zaiser1,2, J. Hartwig1,2, D. Schlippert1,2, V. Lebedev1,2, W. Ertmer1,2, and E.

M. Rasel1,2

1Institute of Quantum Optics, Leibniz Universitat Hannover, Welfengarten 1, 30167Hannover, Germany

2Centre for Quantum Engineering and Space-Time Research - QUEST, Cluster ofExcellence, Welfengarten 1, 30167 Hannover, Germany

We describe the creation of a quantum degenerate gas of Rb atoms in a single beamoptical dipole trap at a wavelength of 1960 nm formed by a Thulium-doped fiber laserwith 50 W output power. First, we study the loading of this dipole trap and find initialtemperatures of the atomic cloud in the dipole trap as low as 2 µK, one order of mag-nitude below values achieved so far by means of simple polarization gradient cooling.We attribute these very low temperatures to a very favorable combination of the nearresonant cooling light and the very far-off-resonant dipole trap laser field. The atomicsource for loading the dipole trap consists of a two-stage design, where a three dimen-sional magneto-optical trap (3D MOT) is loaded by a 2D MOT. With this setup, wereach a very quick loading (less than 1 second) with high initial atom numbers and highphase space densities in the dipole trap.

Forced evaporative cooling is then performed by continuously reducing the laserpower of the dipole trap, thus allowing the hottest atoms to escape the trap. However,this power reduction also leads to a decrease of the already weak confinement of theatoms along the axial direction of the trap and thus an eventually vanishing efficiencyof the forced evaporation. We describe the development of a new trap configuration tocounteract this reduction of the axial confinement. This new trap potential consists ofthe sum of the single beam dipole trap and the weak magnetic quadrupole field of the3D MOT. The efficiency of evaporation could be increased significantly in this weakhybrid trap as compared to the single beam dipole trap and therefore enabled the firstcreation of a Bose-Einstein condensate of 104 Rb atoms in an optical dipole trap of thiswavelength.

This work is motivated by the ultra-low temperatures feasible in BEC, thus possi-bly improving the accuracy of matter wave interferometers for precision measurements,such as e.g. the quantum test of the equivalence principle. Optical dipole traps make afast production of BEC possible allowing for a high repetition rate in an interferometer.Additionally, dipole traps are able to trap all mF -substates, especially mF = 0, beinginsensitive to magnetic fields in first order.


Demonstration of Rydberg blockade between atoms inan optical lattice

Zhanchun Zuo1, Tomoki Watanabe1, Miho Fukusen1, Daisuke Okuyama1,Shuichi Hirai1, Ken’ichi Nakagawa1,2

1Institute for Laser Science, University of Electro-Communication2Japan Science and Technology Agency, CREST, Saitama, Japan

Due to the weaker interactions between ground state neutral atoms, it is very difficultto realize entanglement between neutral atoms. Atoms in highly excited Rydberg stateshave large transition dipole moment that causes the strong dipole-dipole interaction be-tween atoms. Because of this strong dipole-dipole interaction, when several atoms aresufficiently close together the presence of a single excited atom can cause a shift in theenergy of all other atoms which is large enough to prevent resonant excitation of morethan one atom in a sample. This so-called ”Rydberg dipole blockade” has been demon-strated with two atoms separated by more than 1 micron 1 2. This provides a good tool torealize quantum information processing such as quantum gates and entanglement proto-cols. The basic necessity in order to realize the dipole blockade effect is the excitationof atoms from the ground state to a Rydberg state. Very recently, several groups haverealized this Rabi oscillation2 3 4.

Our group is interested in atom Rydberg interactions in the far-off-resonance op-tical dipole trap. Recently, we have prepared a single atom in the dipole trap and thendemonstrate its coherent excitation to a Rydberg state. We have realized Rabi oscillationbetween ground and Rydberg states (n=43) with a single and two cold 87Rb atoms in asmall dipole trap5. Comparing Rabi oscillations of single atom and two atoms for n=43Dand n=75D excited state, we preliminarily got the Rydberg blockade for highly excitedatoms in a dipole trap. This is required step for future demonstrations of the entangle-ment, 2-qubit quantum gates and so on. Now we can observe several separated atomsindependently with a very strong standing wave potential; next we will fix the distancebetween atoms and get Rydberg blockade visually by the image from the camera.

1E. Urban, T. A. Johnson, T. Henage, L. Isenhower, D. D. Yavuz, T. G. Walker, and M. Saffman, “Obser-vation of Rydberg blockade between two atoms,” Nature Physics, 5, 110–114 (2009).

2A. Gaetan, Y. Miroshnychenko, T. Wilk, A. Chotia, M. Viteau, D. Comparat, P. Pillet, A. Browaeys, andP. Grangier, “Observation of collective excitation of two individual atoms in the Rydberg blockade regime,”Nature Physics, 5, 115–118 (2009).

3T. A. Johnson, E. Urban, T. Henage, L. Isenhower, D.D. Yavuz, T. G. Walker, and M. Saffman, “Rabioscillations between ground and Rydberg states with dipole-dipole atomic interactions,” Phys. Rev. Lett. 100,113003 (2008).

4M. Reetz-Lamour, T. Amthor, J. Deiglmayr, and M. Weidemuller, “Rabi oscillations and excitation trap-ping in the coherent excitation of a mesoscopic frozen Rydberg gas,” Phys. Rev. Lett. 100, 253001 (2008).

5Z. Zuo, M. Fukusen, Y. Tamaki, T. Watanabe, Y. Nakagawa and K. Nakagawa, “Single atom Rydbergexcitation in a small dipole trap,” OPTICS EXPRESS, 17, 22898 (2009).

Quantum Information Th 114 523

Extending Coherence of Nitrogen-Vacancy in DiamondL.P. McGuinness1, L.T. Hall1,2, A. Stacey1, D.A. Simpson1,2, J. Orwa1, C.D. Hill1,2,

S. Prawer1, F. Jelezko3, R.E. Scholten1,4 and L.C.L. Hollenberg1

1School of Physics, University of Melbourne, Vic 3010, Australia.2CQCT Centre for Quantum Computer Technology, School of Physics, University of

Melbourne, Vic 3010, Australia.33. Physikalisches Institut, Universitat Stuttgart, Pfaffenwaldring. D-70550 Stuttgart,

Germany.4ARC Centre of Excellence for Coherent X-ray Science, School of Physics, University

of Melbourne, Vic 3010, Australia.

Nitrogen-Vacancy (NV) colour centres in diamond are gaining popularity as solid statequbits due to their exceptional coherence times at room temperature and convenient op-tical readout. Centers deep within ultrapure diamond have coherence times > 1ms1

allowing coherent coupling over large distances2. However, the challenge remains tocreate NV on demand and in specialised devices whilst maintaining these advantageousproperties. For example, long coherence times enable 0.5 µT Hz−1/2 sensitivity3 formagnetometry at nanometer scale, yet incorporation of NV into useable sensors andphotonic devices inevitably leads to a reduction of coherence. Scalable architecturesfor quantum computing also require precise positioning of qubits. We investigate novelmethods for extending coherence times of implanted centers in bulk crystal and nan-odiamonds. Uhrig pulse sequences are used to optimally decouple NV from the envi-ronment and the local spin bath is modified in order to increase coherence times. Theconsequences for quantum information and magnetometry are discussed and recent ex-perimental progress presented.

Po

pu

lati

on

Time (ns)

Po

pu

lati

on

Time (us)

a) b)

Figure 1: a) Rabi oscillations of a single implanted NV center in ultrapure diamond.b) NV decoherence profiles from Uhrig pulse sequences.

1Balasubramanian, G. et al. Ultralong spin coherence time in isotopically engineered diamond. NatureMater. 8, 383-387 (2009).

2Neumann, P., Kolesov, R. Quantum register based on coupled electron spins in a room-temperature solid.et al. Nature Phys. 6, 249-253 (2010).

3Maze, J. R. et al. Nanoscale magnetic sensing with an individual electronic spin in diamond. Nature 455,644-647 (2008).

524 Th 115 Quantum Information

Quantum interference of photons emitted by tworemotely trapped atoms

W. Rosenfeld1, J. Hofmann1, F. Henkel1, M. Krug1, C. Kurz1, M. Mueller1,M. Weber1, H. Weinfurter1,2

1Faculty of Physics, Ludwig-Maximilians-Universitaet, D-80799 Munich, Germany2Max-Planck-Institute of Quantum Optics, D-85748 Garching, Germany

Entanglement between atomic quantum memories at remote locations is a key resourcefor future applications in quantum communication. Here we present our recent progresson establishing entanglement between two single Rb-87 atoms over a large distance.For this purpose we have set up two independently operating atomic traps situated intwo neighboring laboratories (separated by 20 meter). On each side we capture a singleneutral Rb-87 atom in an optical dipole trap and generate a spin-entangled state1 betweenthe atom and a photon. The emitted photons are collected with high-NA objectivesinto single-mode optical fibers and guided to a non-polarizing 50-50 fiber beam-splitterwhere they interfere.

After interference, the two photons leaving the output ports of the beam-splitter aredetected by avalanche photodetectors. We observe bunching of indistinguishable pho-tons, i.e. photons of the same polarization go preferentially into the same output port.First measurements show a bunching ratio of 1:3 with respect to orthogonally polarizedphotons which do not interfere. This bunching allows to perform a Bell-state measure-ment on the photons. By analyzing the polarization we are able to detect two out of fourBell-states (heralded by coincident detection of two photons in particular combinationsof the four detectors), thereby projecting the atoms into an entangled state.

atom 1

PBS

fiber-BS

atom 2

ï¯ñ

excita

tio

np

uls

e

ïñ

APDs

20 m

opticalfiber

Figure 1: Two single atom traps at a distance of 20 m are connected via opticalfibers. The emitted single photons interfere on a 50-50 beamsplitter and are detected bysingle photon counting avalanche photodetectors (APDs). The inset shows the schemefor generation of single photons whose polarization is entangled with the atomic spin.

1J. Volz et al., Phys. Rev. Lett. 96, 030404 (2006).


EIT in warm atomic vapors: beyond the Λ schemeapproximation

M. Scherman, O. Mishina, S. Burks, P. Lombardi, L. Giner, J. Laurat, E. Giacobino

Laboratoire Kastler Brossel, Universite Pierre et Marie Curie, ENS and CNRS,4 Place Jussieu, Case 74, 75252 Paris Cedex 05

The quantum memories that are developed at Laboratoire Kastler Brossel are based onElectromagnetically Induced Transparency (EIT) in atomic ensembles 1. The coherentinterface between the input signal light and the matter is achieved by dynamically con-trolling a strong resonant control field. As the signal field propagates through the atomicmedium, the group velocity is adiabatically reduced to zero, the quantum state beingconverted from a purely photonic state to a matter-like collective spin coherence. Whenthe control field is reactivated, after a user-defined delay, the collective spin is coher-ently converted back into a photonic mode. Using this technique, our group has recentlydemonstrated the storage and retrieval of small coherent states, in a warm vapor of ce-sium atoms. Simultaneous storage of non commuting quadratures has been achievedwith a retrieving excess noise lower than 1%, making it compatible with quantum oper-ation 2.

Later study consisted in modeling in detail the influence of the hyperfine structureof the upper level of the D2 transition of cesium used in the experiment. Due to thisstructure, the EIT behavior is different from what it is in a simple Lambda system (twoground states and one excited state), and is very detrimental in warm vapors configura-tion.

While nonmoving atoms behave as perfectly transparent in the EIT conditions, somenon zero velocity class atoms can induce extra absorbtion. Atoms that perceive a suffi-cient Doppler shift are involved in an off-resonant Raman process which induces absorp-tion of light. Nevertheless, in a three levels atoms, transparency should be preserved atperfect two photon resonance for the control and signal fields. Indeed, the Raman tran-sitions occur for small but non zero two photon detuning for the two fields. Thus, theeffect of transparency is kept for all velocity classes at two photon resonance. In D2 line,due to the presence of several excited states (hyperfine structure), this Raman transitionis frequency shifted. It can occur at two photon resonance for some velocity classes,which destroys the expected transparency.

To improve the EIT in vapors, we proposed an effective cooling mechanism throughoptical pumping. The aim was to burn a hole in the velocity distribution by addingpumping field judiciously detuned, such as to remove selectively the detrimental ab-sorbing atoms. The predicted effect has been experimentally demonstrated in our lab,and significative enhancement of the EIT transparency has been observed.

1M. Fleischhauer and M. D. Lukin, Phys. Rev. Lett. 84, 5094 (2000).2J. Cviklinski et al., Phys. Rev. Lett., 101, 133601 (2008).


Deterministic resolution single ion sourceW. Schnitzler2, G. Jacob1, R. Fickler3, N. Linke4, F. Schmidt-Kaler1, and K. Singer1

1Universitat Mainz, Institut fur Quantenphysik, Staudingerweg 7, D-55128 Mainz,Germany

2Universitat Ulm, Institut fur Quantenmaterie, D-89069 Ulm, Germany3Universtat Wien, Institut fur Quantenoptik, Quantennanophysik &

Quanteninformation, Boltzmanngasse 5, A-1090 Wien, Austria4Department of Physics, University of Oxford, Clarendon Laboratory, Oxford, U.K.

Within the next 5 years the increasing miniaturization of semiconductor devices mightlead to dopant counts of less than one hundred in the channel regions of field effect tran-sistors1. Conventional dopant techniques would then lead to high statistical fluctuationsof dopants causing device parameters to vary at an unacceptable level. Ultimately, at thesingle atom limit, quantum devices like future quantum processors and future nano solidstate devices call for new deterministic production techniques with nanometer. Basedon a segmented ion trap with mK laser cooled ions we have realized a novel determin-istic single ion source which can operate with a huge range of sympathetically cooledion species, isotopes or ionic molecules (Fig. 1 left). We have deterministically ex-tracted a predetermined number of ions on demand (Fig. 1 right) and have measured alongitudinal velocity uncertainty of 6.3m/s and a spatial beam divergence of 600 µrad2. We show in numerical simulations that if the ions are cooled to the motional groundstate (Heisenberg limit) nanometer spatial resolution can be achieved with optimized ionoptics 3. First experimental results of the imaging systems are presented 4.

Figure 1: Left: A segmented linear Paul trap as a deterministic single ion source.Right: Fluorescence images of single ion and of ion crystals and time-of-flight traces.

1Semiconductor Industry Association. The International Technology Roadmap for Semiconductors, 2007edition. SEMATECH:Austin, TX, 2007.

2W. Schnitzler, N. M. Linke, R. Fickler, J. Meijer, F. Schmidt-Kaler, and K. Singer, Phys. Rev. Lett. 102,070501 (2009) 253001.

3R. Fickler, W. Schnitzler, N. M. Linke, F. Schmidt-Kaler, and K. Singer, Journal of Modern Optics 56,2061 (2009).

4W. Schnitzler, G. Jacob, R. Fickler, F. Schmidt-Kaler, K. Singer, arXiv:0912.1258, New Jour. of Physics(2010), in print.


Entanglement detection from interference fringes inatom-photon systems

J. Suzuki1, C. Miniatura2,3, K. Nemoto1

1National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430,Japan

2INLN, UMR 6618, Universite de Nice-Sophia, CNRS; 1361 route des Lucioles, 06560Valbonne, France

3Centre for Quantum Technologies, National University of Singapore, 3 Science Drive2, 117543, Singapore

A measurement scheme for detecting the amount of entanglement in the atomic qubitspinned at given positions is studied by analyzing the interference pattern obtained whenthey emit scalar photons spontaneously 1.

In the case of two qubits, a well-known relation is revisited 2, in which the interfer-ence visibility is equal to the concurrence of the state in the infinite spatial separationlimit of the qubits. For finite distances of two atoms, we study the maximal deviationbetween the visibility and the concurrence by taking into account the superradiant andsubradiant effects. The figure below shows the discrepancy between these two quantitiesas a function of interatomic distance when the purity of the initial state is 1.0, 0.5, 0.1, 0.The result indicates that this deviation is small whenever the qubits are separated bya distance which is a multiple integer of half the wavelength associated to the opticalatomic transition.

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In the case of three qubits, the relations between various entanglement measures andthe interference visibility are studied by analyzing the spontaneous emission processfrom the W-like states to the ground state in the large separation limit of atoms. Aqualitative correspondence among several entanglement measures and the interferencevisibility is discussed. In particular, it is shown that the visibility is directly related tothe maximal bipartite negativity.

1To appear in Phys. Rev. A (arXiv: 1002.4716)2G. Jaeger, A. Shimony, and L. Vaidman, Phys. Rev. A 51, 54 (1995).


Dark Resonances and All Optical Spin Manipulation ofan NV Center in Diamond

E. Togan1, Y. Chu1, J. Maze1, P. Hemmer2, M. Lukin1

1Harvard University, Cambridge, MA, USA2Texas A & M University, Austin, TX, USA

All optical manipulation of spin qubits is a useful tool in quantum control and quantuminformation science since it can be very fast and spatially selective at micrometer lengthscales. We demonstrate that the electronic spin of individual NV centers in diamondcan be initialized, manipulated, and measured all optically. Our approach makes use oflambda-type two-photon transitions recently identified in NV centers1,2. We first showthat optical pumping of dark resonances and coherent population trapping can be usedas a method for initial state preparation of the electronic and nuclear spin. We furtheruse off-resonant optical excitation of the lambda system to obtain unitary rotations ofthe electronic spin.

1C. Santori, et al., Phys. Rev. Lett. 97, 247401 (2006).2see poster by E. Togan, et al., “Quantum entanglement between an optical photon and a solid state spin

qubit.”


Design of quantum Fourier transforms and quantumalgorithms by using circulant Hamiltonians

B.T. Torosov1,2, N.V. Vitanov1

1Department of Physics, Sofia University, James Bourchier 5 blvd, 1164 Sofia, Bulgaria2Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS 5209, BP 47870,

F-21078 Dijon, France

Quantum information processing is built upon sequences of special unitary transforma-tions. One such transformation is the quantum (discrete) Fourier transform (QFT)1. QFTis a key ingredient of many quantum algorithms, including Shor’s factoring algorithm1,2,the quantum phase estimation algorithm1 and the discrete logarithms computing1. There-fore, in order to realize these algorithms, we need to have an efficient method for makingQFT. Traditionally, the QFT is implemented by a quantum cirquit consisting of a largenumber of Hadamard gates and controlled phase shift gates.

We propose to construct QFT by using a special class of Hamiltonians, having acirculant symmetry. These Hamiltonians have the advantage that their eigenvectors arethe columns of the discrete Fourier transform, and they do not depend on the particularelements of the Hamiltonian, as far as the symmetry is conserved. This important fea-ture makes techniques based on circulant Hamiltonians robust against variations in theinteraction parameters3.

In order to realize QFT, we use a special time-dependent Hamiltonian H(t), whichcoincides with a circulant matrix at a final time tf ,

H(tf ) = Hf , (2)

where Hf has a circulant symmetry. If we demand adiabatic evolution for our system,it will end in an eigenstate of the Hamiltonian, and it will realize the QFT. The Hamil-tonian H(t) in the initial moment ti is a diagonal matrix with energies that must not bedegenerate:

H(ti) = diag(E1, E2, . . . , EN ), (3)

where N is the dimension of the Hilbert space we are using. In such way we ensure thatthe evolution is adiabatic and there are no nonadiabatic transitions between the adiabaticstates.

Some systems, which could implement these circulant Hamiltonians (for N = 4),are the following. First, a J = 1/2 ↔ J = 1/2 system, interacting with two linearlypolarized fields in perpendicular directions, the second one seen as a superposition oftwo circularly polarized fields (σ+ and σ−). Another possible system is the so called“diamond”. It is a J = 0 ↔ J = 1/2 ↔ J = 0 system, interacting with two circularlypolarized fields.

1M. A. Nielsen, and I. L. Chuang, Quantum Computation and Quantum Information, (Cambridge Univer-sity Press, 2000), Cambridge ed.

2P.Shor, Proceedings 35th Annual Symposium on foundations of computer science, 124 (1994).3R. G. Unanyan, B. W. Shore, M. Fleischhauer, and N. V. Vitanov, Phys. Rev. A 75, 022305 (2007).


A Quantum Turing MachineJ. H. Wesenberg1 Z. Kurucz2 K. Mølmer2

1Centre for Quantum Technologies, National University of Singapore, Singapore2The Lundbeck Foundation Theoretical Center for Quantum System Research,

Department of Physics and Astronomy, University of Aarhus, Denmark

5μm

L=λ≈25 m

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N@C60

Tape: Spin ensemble Mill: Cooper pair box

Drive: Magnetic gradient

Head: Stripline cavity

We study a recently proposed quantum information processing platform based on anelectron spin ensemble coupled to a coplanar waveguide resonator1. We are particularlyinterested in the shear effect that is observed when a magnetic field gradient is applied tothe spin ensemble while it is interacting strongly with the cavity, as illustrated in Fig. 2.

The shear effect should be observable in a number of physical systems where aninhomogeneously broadened ensemble of independent subsystems interact with a cen-tral system, and where the inhomogeneous broadening can be effectively inverted bye.g. spin echo techniques.

Figure 2: The shear effect.

The cavity interaction gives rise to an en-ergy shift of the superradiant mode of the en-semble, which in effect isolates this particu-lar mode from the ensemble dynamics. Thismodifies the evolution of spin waves as theypass through the region of wavenumber val-ues close to that of the superradiant mode.For certain system geometries the disturbancedoes not lead to any diffusion in wavenumberspace, but can be accurately described by ashear in the wavenumber evolution.

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1J. H. Wesenberg, A. Ardavan, G. A. D. Briggs, J. J. L. Morton, R. J. Schoelkopf, D. I. Schuster andK. Mølmer,“Quantum computing with an electron spin ensemble.” Phys. Rev. Lett., 103, 070502 (2009).


Remote Spin Coupling and Room TemperatureQuantum Computation in NV Diamond CentersN.Y. Yao1, L. Jiang2, A.V. Gorshkov1 G. Giedke3 I. Cirac3 M.D. Lukin1

1Harvard University, Cambridge, MA, USA2California Institute of Technology, Pasadena, CA, USA

3Max-Planck-Institut fur Quantenoptik, Garching, Germany

We propose an experimentally feasible architecture for a room-temperature solid-state quantum computer utilizing nitrogen-vacancy (NV) defects in diamond as qubitsand demonstrate the possibility of high fidelity operations. At an implantation spacingof 20nm, magnetic dipole-dipole interactions are sufficiently strong to enable coherentcoupling of qubits. We further investigate remote spin coupling as a candidate for re-ducing the experimental constraints on such implementations. This approach makes useof a two-dimensional array of nitrogen impurities with sparsely implanted NV centerqubits. By utilizing nitrogen impurities to mediate quantum state transfer, it is possibleto coherently couple spatially separated qubits using SWAP gate, spin chain, and quan-tum mirror techniques. Finally, we show that perfect state transfer is possible throughcompletely thermal spin chains of arbitrary length using only Hamiltonian evolution.


High efficient loading of two atoms into a microscopicoptical trap by using a spatial light modulator

Xiaodong He1,2,3, Peng Xu1,2,3, Jin Wang1,2, Mingsheng Zhan1,2,∗

1State Key Laboratory of Magnetic and Atomic and Molecular Physics, WuhanInstitute of Physics and Mathematics, Chinese Academy of Sciences - Wuhan National

Laboratory for Optoelectronics, Wuhan 430071, China2Center for Cold Atom Physics, Chinese Academy of Sciences, Wuhan 430071, China

3Graduate University of the Chinese Academy of Sciences, Beijing 100049, China∗corresponding author: [email protected]

We demonstrate a approach to transport two individual 87Rb atoms trapped in a two-site ring lattice into a single microscopic far-off resonance trap (MFORT) by utilizinga spatial light modulator (SLM). We employ our recently developed technique of dy-namically rotating computer generated ring lattice just through displaying the hologramanimation movie on the SLM 1, then we transform ring lattice with l = 1 into a sin-gle microscopic dipole trap. Two atoms initially trapped in the ring lattice are broughtinto single MFORT under the evolution of the computer generated holographic dipoletraps. Our scheme is simple for experimental implementation, and we obtained a suc-cess rate larger than 95% of preparing pairs of atoms in a single MFORT experimentally.Meanwhile, with two atoms in the MFORT we observed a strong two-atom loss uponimposing the resonant light.

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Figure 1: Observed fluorescence of single atoms. Shown in (a) is the fluorescencesignal from the whole two traps in the double well ring lattice . (b) is the fluorescencesignal from atom in the single Gaussian trap. (c) is the accumulated fluorescence signalfrom single trap after two atoms trapped in the ring lattice being injected into singletrap. (d) is the the accumulated fluorescence signal from single trap after single atomstrapped in either part of the ring lattice being inserted into the single trap.

1X. D. He, P. Xu, J. Wang, and M. S. Zhan, “Rotating single atoms in a ring lattice generated by a spatiallight modulator,” Optics Express 17,21007-21014 (2009).

Quantum Optics and Cavity QED Th 124 533

Substantial interaction between a singe atom and afocused light beam

S.A. Aljunid1, J. Lee1, B. Chng1, M. Paesold1,2, D.H. Lan1, Z.W. Teo1,G. Maslennikov1, V. Scarani1, C. Kurtsiefer1

1Centre for Quantum Technologies, National University of Singapore, Singapore2ETH, Zurich, Switzerland

We investigate both theoretically and experimentally the near-resonant interaction be-tween a single atom in an optical dipole trap and a focused light beam. We have demon-strated that even for a moderate focusing strength, a single atom localized at the focusof a simple aspheric lens can scatter a significant fraction of light 1,2, impose a phaseshift 3, and partially reflect a probe beam. With our current experimental system, weobserve an extinction of 10%, a phase shift of about 1 and a reflectivity of 0.17%. Foran optimal focusing geometry, we would expect an extinction up to 92%, and a phaseshift of 30. The strength of an observed effect together with the theoretical predictionssuggests to combine the effects of strong focusing with the well-established methods ofcavity QED. As an example one can consider a cavity which supports a strongly focusedfield mode of the type we obtain with our aspheric lens arrangement 4 (see Fig. 1).

coatingsHR mirror

elliptical surface

Figure 1: Atom-cavity configuration in the strong focusing regime. Outer elliptical sur-faces of the mirrors provides the mode coupling for a numerical aperture of up to 0.3.

Simple estimates show that in such case one should achieve the single photon Rabifrequency few times larger than obtained in the current experiments 5,6 and thus be ableto reduce the Q factor of the mirrors needed to compensate for the losses. This opensnew perspectives in possibility to scale up the system consisting of many ’atom+cavity’nodes for quantum networking due to a significant technical simplification of the atom-light interfaces.

1M. K. Tey, et al., Nature Physics 4, 924 (2008)2M. K. Tey et. al., New J. Phys. 11, 043011 (2009)3S.A. Aljunid et al., Phys. Rev. Lett. 103, 153601 (2009)4S.E. Morrin et al., Phys. Rev. Lett. 73, 1489 (1994)5H.J. Kimble, Physica Scripta 176, 127 (1998)6M. Hennrich et al., Phys. Rev. Lett. 94, 053604 (2005)

534 Th 125 Quantum Optics and Cavity QED

Quadripartite continuous-variable entanglement viaquadruply concurrent downconversion

S. L. W. Midgley1, A. S. Bradley2, O. Pfister3 M. K. Olsen1

1ARC Centre of Excellence for Quantum-Atom Optics, School of Mathematics andPhysics, University of Queensland, QLD 4072, Australia.

2Jack Dodd Centre for Quantum Technology, Department of Physics, University ofOtago, P. O. Box 56, Dunedin, New Zealand.

3Department of Physics, University of Virginia, 382 McCormick Road, Charlottesville,Virginia 22904-4714, USA

We investigate an experimentally feasible intra-cavity coupled down-conversion schemeto generate quadripartite entanglement using concurrent nonlinearities. We verify thatquadripartite entanglement is present in this system by calculating the output fluctua-tion spectra and then considering violations of optimized inequalities of the van Loock-Furusawa type1. The entanglement characteristics both above and below the oscillationthreshold are considered. We also present analytic solutions for the quadrature operatorsand the van Loock-Furusawa correlations in the undepleted pump approximation. Cur-rently, we are investigating a similar scheme2 as a candidate for realizing the simplestfour node cluster state, proposed as a resource for one-way quantum computing.

χ(2)

ω8

ω1

ω2

ω3

ω4

ω5

ω6

ω7

Figure 1: Schematic of a χ(2) crystal inside a pumped Fabry-Perot cavity. Pump lasersdrive four intracavity modes with frequencies ω1, ω2, ω3 and ω4 (represented by circlesand squares), which are down-converted to four output modes with frequencies ω5, ω6,ω7 and ω8.

1P. van Loock and A. Furusawa, Physical Review A 67, 052315 (2003).2H. Zaidi, N. C. Menicucci, S. T. Flammia, R. Bloomer, M. Pysher, and O. Pfister, Laser Physics 18, 659

(2008) and N. C. Menicucci, S. T. Flammia, and O. Pfister, Physical Review Letters 101, 130501 (2008).


Novel Control of Atom-Atom Interactions in a Two-WayCascaded Cavity QED SystemS. Zeeb, C. Noh, A.S. Parkins, H.J. Carmichael

Department of Physics, University of Auckland, Private Bag 92019, Auckland 1142,New Zealand

We present an investigation of a two-way cascaded cavity QED system consisting of twomicrotoroidal resonators, which are connected via an optical fibre. The microtoroidsact as cavities, each with two counter-propagating whispering-gallery modes, and singleatoms are coupled to each of the microtoroids through the evanescent fields leaking fromthese modes. In the bad cavity regime, where the decay rate of the resonator modes ismuch larger than any other rate in the system, a simplified master equation with theresonator modes adiabatically eliminated is derived. From this master equation, weuncover a novel dependence of the effective atom-atom interaction (mediated by thecavities and fibre) on the atom-cavity detuning. In particular, with appropriate choicesof detunings the atoms can be made to experience either collective spontaneous emission(superradiance) or a (coherent) dipole-dipole interaction with single-atom spontaneousemission. This capacity for switching the fundamental nature of the interaction seemsunique to the two-way cascaded system considered and is manifested in the spontaneousemission spectrum.


Ground-state Quantum Beats in Cavity QEDD.G. Norris1, A. Cimmarusti1, L.A. Orozco1, P. Barberis-Blostein2, H.J. Carmichael3

1Joint Quantum Institute, University of Maryland and NIST, College Park, Maryland,USA

2IIMAS, Universidad Nacional Autonoma de Mexico, Mexico DF, Mexico3Dept. of Physics, University of Auckland, Auckland, New Zealand

We present measurements of optical correlations from a driven high-finesse cavitytraversed by a continuous cold beam of 85 Rb atoms. The combination of two modesof orthogonal light polarization with the magnetic structure of the atoms allows us toseparate photons originating from spontaneous emission from those that come from thedriving laser. The second-order intensity correlation function reveals quantum beats attwice the ground-state Larmor frequency for a small applied magnetic field. The beatsarise from ground-state superpositions generated in the spontaneous emission cycles,between magnetic sublevels in a single atom, and between the levels of multiple atoms.In addition, the mixing in of a small amount of coherent drive light before detectionallows us to measure a homodyne contribution at the single Larmor frequency. Thecoherences survive many cycles of spontaneous emission and optical pumping. Thefrequency of oscillation is sensitive to different parameters of the system; we report apower-dependent accumulation of phase from sponanteous emission events that exactlyreverses the sign of the normal AC Stark shift in the ground state. We present the resultsof modeling the atomic beam and interactions in a quantum trajectories simulation withthe full magnetic structure and many simultaneous atoms, and from this extract the formof the various coherent processes that make up the averaged signal. Work supported byNSF of the USA, CONACYT Mexico, and the Marsden Fund of the RS of NZ.


Quantum phase transition of nonlinear light in the finitesize Dicke Hamiltonian

B. M. Rodrıguez-Lara, R.-K. Lee

Institute of Photonic Technologies, National Tsing-Hua University, Hsinchu 300,Taiwan.

We study the quantum phase transition of a N two-level atomic ensemble interactingwith an optical degenerate parametric process, which can be described by the finite sizeDicke Hamiltonian plus counter-rotating and quadratic field terms. Analytical closedforms of the critical coupling value and their corresponding separable ground states arederived in the weak and strong coupling regimes. The existence of bipartite entangle-ment between the two-level-system ensemble and photon field as well as between en-semble components for moderate coupling is shown through numerical analysis. Givena finite size, our results also indicate the co-existence of squeezed fields and squeezedatomic ensembles.

Figure 1: Phase diagram of the studied Hamiltonian, H = hωf a†a + hωaJz +

h λ√N(a + a†)Jx + hκ(a + a†)2, in the parameter space of the linear photon-atom

coupling strength, λ, and the nonlinear photon-photon interaction strength, κ. (a) Themean value for the atomic z-component, ⟨Jz⟩, (b) the average photon number for thefield, ⟨n⟩, (c): the bipartite concurrence, and (d) the entropy of entanglement, ⟨S⟩, arecalculated for the case of N = 2. The corresponding minima and maxima values for thecolor legend are shown below. The field photon number and atomic angular momentumprobability distributions along the solid line in (c) are shown in (e-h) and (i-l), orderedaccording to the markers A-D, respectively.


Entanglement between internal and external degrees offreedom of a driven trapped atom

M. Roghani, H.P. Breuer, H. Helm

Institute of Physics, Albert-Ludwigs University, Hermann-Herder-Strasse 3, D-79104Freiburg, Germany

The dynamics of a Λ-shaped trapped atom, driven by two lasers to conditions approach-ing electromagnetically-induced transparency (EIT), is studied numerically via the quan-tum Markovian master equation1,2. The analysis of the solutions of this equation allowsto investigate the nature of dissipative processes which are responsible for EIT cooling3.

The numerical approach gives us the possibility to investigate the dynamics of theentanglement between electronic and vibrational degrees of freedom and the quantummutual information. Far from the Lamb-Dicke limit an intricate behavior of these quan-tities is found, as well as the emergence of a mixed entangled non-equilibrium stationarystate4. An example of our numerical calculations is shown in Fig. 1. The initial con-ditions (t = 0) is that the atom is in electronic state |1⟩ and in vibrational level n = 5.After 3 ms the mean vibrational quantum number of the atom is ⟨n⟩ = 0.02. Duringthe cooling process the death and revival of negativity is observed. Moreover, the nu-merical simulation allows the determination of the degree of non-Markovianity of thedynamics5.

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1M. Roghani, and H. Helm, Phys. Rev. A 77, 043418 (2008)2H. P. Breuer, and F. Petruccione,The Theory of Open Quantum Systems (Oxford Univ. Press, Oxford,

2007)3M. Roghani, H.-P. Breuer, and H. Helm, Phys. Rev. A 81, 033418 (2010)4M. Roghani, H. Helm, H.-P. Breuer, To be published in Physica Scripta5H. P. Breuer, E. M. Laine, and J. Piilo, Phys. Rev. Lett 103, 210401 (2009)


Using noise to improve atom-cavity couplingA. Auffeves1, D. Gerace2, J.M. Gerard3 M.F. Santos4,5 C.L. Andreani2 J.P. Poizat1

1Institut Neel-CNRS, Grenoble, France2Dipartimento di Fisica “Alessandro Volta,” Universita di Pavia, Pavia, Italy

3CEA/INAC/SP2M, Grenoble, France4Departamento de Fısica, UFMG, Belo Horizonte, Brazil

5Centre for Quantum Technologies, Singapore

Most of the time, noise and the consequent decoherence are considered villains to theobservation of fundamental quantum aspects and the production of quantum devices.In this work1 we present a counter-example with very interesting potential applicationsboth in cavity QED and nanophotonics. First, we describe in general terms the dynamicsof an incoherently and off-resonantly pumped single emitter coupled to a cavity field inthe presence of pure dephasing and dissipation. Then we analyze this system both whenit is dominated by spontaneous emission and when stimulated emission plays a crucialrole.

In the first scenario, we show that the two systems behave like two quantum boxesexchanging excitations and we derive an effective coupling constant for this exchangethat depends on both their coherent and incoherent properties. This effective rate thendefines a generalized Purcell factor for the atom which is also essential to determine therate of emitted photons in the cavity mode if the atom is continuously pumped. Bothquantities are maximized when atom and cavity are in resonance, i.e. any detuning actsnegatively on both of them. However, we show that if the two systems are detuned, theaddition of pure dephasing noise can partially compensate for the off-resonance effectimproving the system’s capacity to generate single photons on demand.

In the second scenario, we consider an atom that is strongly pumped and also coher-ently exchanges photons with the cavity field. We show that ideal single emitter lasingconditions are achievable in resonance, and detuning tends to spoil them. However,in the presence of detuning, once again, pure dephasing comes to the rescue, helpingrestoring the lasing regime.

The formalism developed is general and can be applied to any system composedof a two-level oscillator and a cavity field, be it in atomic or superconducting CQED,solid state nanophotonics, and so on. The general conclusion is that noise and decoher-ence can also play positive roles in such systems allowing for the study of fundamentalphysics and the development of new and more efficient quantum devices.

1A. Auffeves, D. Gerace, J.M. Gerard, M.F. Santos, C.L. Andreani, J.P. Poizat, to be published in Phys.Rev. B


Multi-Photon Blockade in Cavity QEDS.S. Shamailov1, A.S. Parkins1, M.J. Collett1, H.J. Carmichael1,2

1Department of Physics, University of Auckland, Private Bag 92019, Auckland, NewZealand

2Joint Quantum Institute, Department of Physics, University of Maryland and NationalInstitute of Standards and Technology, College Park, MD 20742, USA

The driven Jaynes-Cummings model is studied in the strong-coupling, strong-drive regimeby way of numerical simulations. The investigation is motivated by recent advancesfrom Circuit QED which show conclusively that the model and parameter regimes con-sidered are experimentally feasible. The focus is on the multi-photon transitions tohigher excitation dressed-states, as observed by Bishop et al.1. Photon statistics ofthe light leaking out of the cavity are examined when the laser is tuned to such amulti-photon resonance. We find that with increasing drive strength, bunched, super-poissonian light is transformed into antibunched and sub-poissonian light. These resultsare interpreted and a simple model is constructed to explain our observations analyti-cally. Moreover, the incoherent spectrum is computed, leading to observation of a sat-uration effect and multiple dynamic Stark splittings, resulting in a Mollow triplet. Thisis interpreted analogously to resonance fluorescence in the context of Floquet theoryand the simplest example is treated analytically. In summary, we observe Multi-PhotonBlockade.

1Lev. S. Bishop et al., Nonlinear response of the vacuum Rabi resonance, Nature Physics, 4, 12 (2008).


Strong Interactions of Single Atoms and Photons near aDielectric Boundary

N.P. Stern1, D.J. Alton1, T. Aoki1, H.S. Lee2, E. Ostby2, K.J. Vahala2, H.J. Kimble1

1Norman Bridge Laboratory of Physics, California Institute of Technology 12-33,Pasadena, CA 91125, USA

2T. J. Watson Laboratory of Applied Physics, California Institute of Technology,Pasadena, California 91125, USA

Strong coupling in cavity quantum electrodynamics (cQED) between atoms and micro-toroid resonators1 allows for coherent interactions between matter and light to dominateover irreversible channels of dissipation in a scalable on-chip quantum node with highphotonic coupling2. Using such microresonators as nodes in a quantum network suitablefor large-scale quantum information processing3 necessitates localizing individual atomson distance scales ∼100 nm from a resonator’s surface where atoms experience signif-icant van der Waals interactions with the dielectric boundaries of the resonator. Here,we study the dynamics of cesium atoms strongly coupled to a microtoroidal cavity ina regime where atomic motion is influenced by surface interactions with the dielectricresonator. We utilize fast logic electronics to achieve real-time detection in 250 nanosec-onds of falling atom transit events of duration 2-4 microseconds followed by conditionalswitching of the cavity input beam while the atom is coupled to the cavity. Laser probedetuning after atom detection enables measurement of the cQED response in both thetemporal and spectral domains, allowing observation of vacuum Rabi splitting. We em-ploy these strong atom-cavity interactions to probe the significant role of van der Waalsattraction on the motion of an atom through the evanescent field of the resonator. Ourwork offers a first step toward trapping atoms near the surface of micro- and nano-scopicoptical resonators for applications in quantum information science.

We thank NSF, the DoD NSSEFF program, ARO, and IARPA for financial support.

(a) (b)

Figure 1: Simulated trajectories transiting by a microtoroid for probe frequency (a)red-detuned and (b) blue-detuned from the atomic transition. For red detuning, all de-tected atoms crash into the dielectric surface due to dipole and van der Waals attraction,while for blue detuning some are deflected by the dipole force.

1D. K. Armani, T. J. Kippenberg, S. M. Spillane, and K. J. Vahala. “Ultra-high-Q toroid microcavity on achip.” Nature 421, 925-928 (2003)

2T. Aoki, B. Dayan, E. Wilcut, W. P. Bowen, A. S. Parkins, T. J. Kippenberg, K. J. Vahala, and H. J. Kimble“Observation of strong coupling between one atom and a monolithic resonator.” Nature 443, 671-674 (2006)

3H. J. Kimble. “The quantum internet.” Nature 453, 1023-1030 (2008)


Multipartite entanglement production using feedbackR. N. Stevenson1, A. R. R. Carvalho1,2, J. J. Hope1,2

1Department of Quantum Science, Research School of Physics and Engineering, TheAustralian National University, ACT 0200, Australia

2Australian Centre for Quantum-Atom Optics, Department of Quantum Science,Research School of Physics and Engineering, The Australian National University, ACT

0200, Australia

The production and manipulation of entangled states has been a major feature of quan-tum information research in the last several years. A problem with producing entangledstates is that decoherence can quickly destroy entanglement. A promising approach todeal with this problem is the use of active quantum feedback control. Recently, wehave shown that direct feedback under the appropriate detection strategy leads to therobust production of highly entangled states of two atoms or ions in a cavity1,2. In thiscontribution we will present our recent progress towards the extension of this model tomultipartite systems.

The system we investigate consists of a chain of two-level atoms equally coupled toa single cavity mode (Fig. 1). The atoms are simultaneously driven by a laser field (notshown) and a photo-detector monitors the leakage of photons from the damped cavity.Every detection event triggers the application of a control Hamiltonian on the atoms.

Figure 1: Schematic view of the system.

It was shown in1 that a quantum jump-based feedback can stabilise the anti-symmetricBell state against different decoherence sources. When more atoms are added, the sym-metry structure gets more complex but control can still be performed on the system. Foreven number of atoms, there are various pure states that are dark states of the system.Due to the multiplicity of stationary states, the system without control, converges to amixture of these states that is not necessarily entangled. The inclusion of a suitablechoice of unitary control is able to isolate the desired entangled state as the only station-ary solution of the problem. With appropriate choice of feedback the maximum steadystate concurrence achieved is around 1.28, slightly below the value of 1.32 for a 4-partiteGHZ state. With six or more particles the steady states have entanglement greater thanthe corresponding GHZ state.

1A. R. R. Carvalho and J. J. Hope, Physical Review A 76, 010301 (2007).2A. R. R. Carvalho, A. J. S. Reid, and J. J. Hope, Physical Review A 78, 012334 (2008).


Cavity QED with single defects in diamond: strongcoupling using superconducting resonators

J. Twamley1, S.D. Barrett1,2

1Centre for Quantum Computer Technology, Physics Department, MacquarieUniversity, Sydney, NSW, Australia

2Blackett Laboratory and Institute for Mathematical Sciences, Imperial CollegeLondon, Prince Consort Road, London SW7 2BZ, United Kingdom

Circuit-QED has demonstrated very strong coupling between light and matter and hasthe potential to engineer large quantum devices 1. Hybrid designs have been proposedwhich couple large ensembles of atomic and molecular systems to the superconductingresonator 2. We show that one can achieve an effective strong coupling between lightand matter for much smaller ensembles (and even a single electronic spin), through theuse of an interconnecting quantum system: in our case a persistent current qubit 3. Us-ing this interconnect we show that one can effectively magnify the coupling strengthbetween the light and matter by over five orders of magnitude g ∼ 7Hz → 100kHz,and enter a regime where a single Nitrogen-Vacancy electronic spin can shift the cavityresonance line by over ∼ 20 linewidths. With such strong coupling between an individ-ual electronic spin in an NV and the light in the resonator, one has the potential builddevices where the associated NV nuclear spins can be strongly coupled over centimetersvia the superconducting bus.

in out

E(x)

α

NV

3 JunctionPCQ

Ip

B(x)(A) (B)

Figure 1: Strong coupling of a single Nitrogen-Vacancy electronic spin to a mi-crowave photon trapped in a superconducting coplanar resonator. (A) Schematic of NVencircled by a Persistent Current Qubit (PCQ) next to a coplanar resonator, (B) Cavityspectrum indicating the splitting of the resonance lines due to the NV as one shrinks thePCQ loop.

1A. Blais, R. Huang, A. Wallraff, S. Girvin, and R. Schoelkopf, Phys Rev A 69, 062320 (2004); L. DiCarlo,J. M. Chow, et al., Nature 460, 240 (2009)

2A. Andre, et al, Nat. Phys. 2, 636 (2006); A. Imamoglu, Phys. Rev. Lett. 102, 083602 (2009); J. H.Wessenberg et al, Phys. Rev. Lett 102, 083602 (2009); D. Marcos et al, arXiv: 1001.4048

3J. Twamley, S.D. Barrett, arXiv: 0912.3586, accepted to Phys. Rev. B


Quantum Non-Demolition Measurement in aRadio-Frequency High Density Atomic Magnetometer

G. Vasilakis, P. Vachaspati, M.V. Romalis

Department of Physics, Princeton University, Princeton, New Jersey 08544, USA

Quantum Non-Demolition (QND) measurements have attracted a great deal of inter-est for extending the precision of measurements beyond the standard quantum limits.We implement and study a QND scheme in a radio-frequency atomic magnetometer,operated at high density with hot 39K vapor. A circularly polarized pump beam po-larizes alkali atoms along the direction of a static holding field, and a perpendicularlinearly polarized probe beam measures the amplitude of spin precession through Fara-day paramagnetic rotation. In this scheme, the back-action is generated as a result ofthe probe beam light-shift noise. We use a stroboscopic probe beam that turns on andoff at twice the Larmor frequency to realize a quantum non-demolition Hamiltonian in amanner similar to the one that has been implemented with mechanical oscillators1. Weshow back-action suppression with this method that depends on the duty cycle of theprobe beam and on the detuning of the modulation frequency from twice the Larmorfrequency. We study how the spin-projection noise depends on the longitudinal polar-ization and demonstrate very good agreement with a simple theoretical model. We findthat the unpolarized spin noise offers an excellent standard to calibrate the polarized spinnoise and exclude potential non-quantum mechanical noise sources. We also discuss asituation where the sensitivity of a magnetometer will benefit from the increased band-width that QND measurements offer2. In particular, in high density alkali-metal vaporsthe magnetic sensitivity of an initially fully polarized sample decreases with time as thetransverse relaxation due to spin-exchange collisions between alkali atoms increases.The high bandwidth of the QND magnetometer should allow us to operate efficientlyat short timescales, where the magnetic sensitivity is maximized. We finally show pre-liminary results of spin-noise measurements in a multi-pass cell. Unlike a cavity, it hasa large active volume and is very robust and easy to implement. We demonstrate spinnoise measurements with 38 passes with corresponding increase in the spin noise rel-ative to the photon shot noise. This multi-pass arrangement increases significantly theoptical depth and offers the possibility of higher magnetic field sensitivity and strongersqueezing.

1R. Ruskov, K. Schwab, and A. N. Korotkov, Phys. Rev. B 71, 235407 (2005)2V.K. Shah, G. Vasilakis, and M.V. Romalis, Phys. Rev. Lett. 104 013601 (2010)


Cavity-Assisted Nondestructive Measurement ofRabi-Oscillations

Jurgen Volz, Roger Gehr, Jerome Esteve, Jakob Reichel

Laboratoire Kastler-Brossel, ENS, CNRS, UPMC, Paris, France

The coherent interaction between a quantum-mechanical two-level system and electro-magnetic fields is the basic ingredient of most quantum optical experiments. Appli-cations like atomic clocks directly rely on the observation of Rabi-oscillations of anatomic ensemble induced by microwave radiation. These oscillations are routinely ob-served in a large variety of quantum systems. However, measurement backaction usuallydestroys the coherence of the system, and the oscillations can not be observed in a singlerun. Therefore, a large number of experimental repetitions is required to reconstruct thefull oscillation. Recently, the nondestructive observation of Rabi-oscillations has beendemonstrated using large ensembles of approximately 106 cold Cs atoms1,2.

In our experiment we use a fiber-based high-finesse cavity on an atomchip3 to di-rectly observe Rabi-oscillations between the two ground state hyperfine states of smallensembles containing less than 1000 ultracold 87Rb atoms. We investigate the transitionfrom the ’classical’ regime, where we non-destructively observe the Rabi-oscillations ofa few 100 atoms, to the quantum regime, where the oscillations are suppressed due tothe quantum Zeno effect.

87Rb

AlN ceramic substrate

HR coated, concave fiber endfacets

Singlemode fiber Multimode fiber

microfabricatedAu wires

probe light to APD

Figure 1: Experimental setup. A microfabricated fiber cavity on an atomchip. Toprepare atomic ensemble inside the cavity, we first generate a small BEC and magneti-cally transfer it into an intracavity standing wave dipole trap. The cavity transmissiondepends on the difference of atomic population in the two hyperfine states allowing thedirect observation of Rabi-oscillations.

1S. Chaudhury, et al., Phys. Rev. Lett. 96, 043001 (2006)2P. J. Windpassinger et al., Phys. Rev. Lett. 100 103601 (2008)3Y. Colombe, et al., Nature 450, 272-276 (2007)

546 Th 137 Quantum Simulators...

Itinerant Ferromagnetism in Cold Fermionic AtomsLoaded on a Two-leg Optical LadderM. Okumura1,2, S. Yamada3,2, M. Machida3,2 H. Aoki4

1Computational Condensed Matter Physics Laboratory, RIKEN, Wako, Saitama, Japan2CREST(JST), Kawaguchi, Saitama, Japan

3CCSE, Japan Atomic Energy Agency, Taito-ku, Tokyo, Japan4Department of Physics, The University of Tokyo, Hongo, Tokyo 113-0033, Japan

It has been known, in the field of correlated electron systems, that the way in whichcorrelation effects appear is dominated by the lattice structure. One such quantum phaseis itinerant ferromagnetism, for which a full understanding is yet to come, so that the coldfermionic atom systems are an ideal test-bench. Three mechanisms have been known foritinerant ferromagnetism, i.e., Stoner’s, Nagaoka’s, and flat-band mechanisms1. The firstone has been reported in an ultra-cold atom experiment recently2, while the latter two,mutually related, have not been realized. Realization of the flat-band ferromagnetism,arising in dispersionless bands with some topological condition, in optical lattice sys-tems is a challenging problem34. However, the lattice structure required for the flat-bandis not so simple. Nagaoka’s ferromagnetism, on the other hand, requires less stringentlattice conditions, but the ferromagnetism in its original formalism requires a pathologi-cal condition, i.e., a single hole in a half-filled band. One manifestation of the pathologyis the fragility of Nagaoka’s state against thermal fluctuations. Subsequently, Nagaoka-related ferromagnetism has been explored for special lattices such as the two-leg ladderthat accommodates finite hole densities and a finite energy gap for the magnetism5.

With this background, here we propose that a stable itinerant ferromagnetism shouldemerge in cold fermionic atoms for finite hole densities in a two-leg ladder optical lat-tice system6. A special interest in the cold atom system is that, on top of the opticallattice potential which should be readily created by a combination of superlattice stand-ing waves of lasers, the atoms feel a trapping potential. This causes the system to havean interesting phase separation into magnetic and nonmagnetic phases in real space. Wediscuss how to create and detect the itinerant ferromagnetism in this system, includingspin-imbalance effects. Specifically, we predict that the system should exhibit the phase-separated magnetism in spin-imbalanced situations, and the phase diagram obtained hereshows that the required strength of correlation is also realistic. So the ferromagnetism isexpected to be observable in ultra-cold atom experiments.

1For a review, see, e.g., H. Tasaki, Prog. Theor. Phys. 99, 489 (1998).2G.-B. Jo et al., Science 325, 1521 (2009).3L. Wang, X. Dai, S. Chen, and X.C. Xie, Phys. Rev. A 78, 023603 (2008).4K. Noda, A. Koga, N. Kawakami, and T. Pruschke, Phys. Rev. A 80, 063622 (2009).5M. Kohno, Phys. Rev. B 56, 15015 (1997).6M. Okumura, S. Yamada, M. Machida, and H. Aoki, in preparation

Quantum Simulators... Th 138 547

Simulation of quantum noise in BECB. Opanchuk1, M. Egorov1, S. Hoffmann2, A. Sidorov1, P. D. Drummond1

1ACQAO, Swinburne University of Technology, Hawthorn, VIC 3122, Australia2ACQAO, Physics Department, University of Queensland, Queensland, Australia

Atom interferometry is at the heart of many suggested future applications of ultra-cold atomic physics. Bose-Einstein condensates or atom lasers have potential advan-tages as detectors or sensors, provided one can extract atomic phase information. How-ever, unlike photons, atoms can interact rather strongly, causing dephasing. An intimateunderstanding of quantum many-body dynamics is essential in understanding the pre-cise nature of interaction-induced dephasing in the measurement process. Progress inthis technology therefore requires a quantitative theory of atom interferometry.

Coupled Gross-Pitaevskii equations are widely used to simulate the dynamics ofBEC. This method is easy and relatively fast, and it allows one to obtain rather accuratepredictions for the evolution of the cloud structure1. The problem is that this methodproduces incorrect results for low number of particles or long evolution times, sinceit neglects quantum noise. There are ways to improve GPE-based simulations, one ofwhich is the inclusion of quantum noise terms via the Wigner representation.

Here, we give a simple, yet quantitatively accurate theoretical approach to calcu-lations of atom interferometry using a truncated Wigner representation. This methodextends the conventional Gross-Pitaevskii equations describing a Bose condensate to in-clude quantum noise effects. We show through comparison with experimental interfero-metric measurements on Bose condensates that the theory predicts observed dephasingresults, within experimental errors. No fitting parameters or added technical noise isrequired in these comparisons. Importantly, we can clearly demonstrate where phasedecay is driven by intrinsic quantum fluctuations due to the effects of a beamsplitter,and where it is driven by trap inhomogeneity or other effects.

The noise can be taken into account by writing the master equation for the conden-sate and transforming it into one of the quasi-probability representations, like positive-P2,3

or Wigner2. The resulting equation can then be expressed as a set of stochastic equa-tions, which can be solved numerically. We present the results of such simulations forseveral types of experiments on 87Rb condensates (namely, two-component clouds of|1,−1⟩ and |2,−1⟩ states in a magnetic trap). In addition, we use the simulation data torevise the values of scattering lengths and loss terms for these components.

1R. P. Anderson, C. Ticknor, A. I. Sidorov, B. V. Hall, Phys. Rev. A, 80:023603 (2009)2M. J. Steel, M. K. Olsen, L. I. Plimak, P. D. Drummond, S. M. Tan, M. J. Collett, D. F. Walls and

R. Graham, Phys. Rev. A, 58(6):48244835 (1998)3J. J. Hope, Phys. Rev. A, 64(5):053608 (2001)

548 Th 139 Quantum Simulators...

Single-Site Probing of the Superfluid-Mott InsulatorTransition with a Quantum Gas Microscope

W. Bakr, E. Tai, R. Ma, J. Gillen, A. Peng, G. Jotzu, J. Simon, S. Folling, M. Greiner

Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

Ultracold gases in optical lattices provide an elegant avenue to controlled, coherent in-teractions between atoms, especially for the realization of strongly correlated phasesof matter. These systems can faithfully mimic the physics of condensed materials un-der much more dilute conditions, permitting more precise control over interactions andpotentials as well as new and unique probes of the resulting ordering.

Here we present the first site-resolved study of the superfluid-Mott insulator transi-tion. Using a Quantum Gas Microscope, we are able to observe, with single-site reso-lution, the shell structure of the Mott insulator, with up to N = 4 atoms per site. Ourhigh single-shot fidelity permits us to observe atom number statistics in a site-resolvedmanner, a tool which we employ to demonstrate squeezing of the atom number distri-bution by more than a factor of 10 beyond the shot-noise limit. We then investigate thetimescale of the SF-MI transition using the degree of squeezing as a probe, and observe asqueezing-adiabaticity timescale of approximately 3 ms, consistent with the interactionU, and not the tunneling J as one might naıvely expect.

Ultra-low entropy domains seem to be an important first step towards realizationof quantum magnets in ultracold atomic systems. To this end, we present evidence ofultra-low entropy Mott domains realized as heterostructures in contact with superfluidbaths.

Figure 1: Single-shot, site-resolved image of a Mott Insulator with shells of up toN = 3 atoms per site. Our imaging method is sensitive to the parity of the site occupa-tion, so N = 1, 3 appear black (i.e. scatter light), and N = 2 appears white (i.e. do notscatter light).

Quantum Simulators... Th 140 549

Versatile Optical Lattices to Control Rydberg AtomInteractions for Uses in Quantum Computing.

K.J. Weegink, E.D. van Ooijen, S.A. Haine, M.J. Davis, H. Rubinsztein-Dunlop

The University of Queensland, School of Mathematics and Physics, Qld 4072, Australia

The long lived quantum levels in the hyperfine manifold of neutral atom ground stateshave long been candidates as qubits for quantum information protocols. However, neu-tral atoms have very short range interactions, so the use of Rydberg atoms, with rel-atively long range interactions (∼10µm), can be used to mediate interactions betweenqubits. Recent experiments with Rydberg atoms have demonstrated entanglement1 andthe implementation of a controlled-NOT gate2.

We propose a scheme to create versatile optical 2D lattices using a scanning beamtrap3 that allows controlled interactions between Rydberg atoms located at different lat-tice sites. The scanning trap involves rapidly moving a tightly focused laser over severalpositions, so that the atoms see a time-averaged potential. The scanning trap positionis controlled using a 2D acousto-optic modulator. The atoms are effectively trapped ina 2D array of optical tweezers, the structure of which can be dynamically changed tobring together, and allow interactions between atoms that are not located adjacent to oneanother in the lattice. The flexibility of this system will allow individual control of asingle lattice site allowing more efficient coding schemes and more refined control overa large number of atomic qubits.

1T. Wilk, A. Gaetan, C. Evellin, J. Wolters, Y. Miroshnychenko, P. Grangier, and A. Browaeys, Phys. Rev.Lett. 104, 010502 (2010).

2L. Isenhower, E. Urban, X. L. Zhang, A. T. Gill, T.Henage, T. A. Johnson, T. G. Walker, and M. Saffman,Phys. Rev. Lett. 104, 010503 (2010).

3S. K. Schnelle, E. D. van Ooijen, M. J. Davis, N. R. Heckenberg, and H. Rubinsztein-Dunlop, Opt.Express. 16, 1405 (2008).

550 Th 141 Spectroscopy

Search for biomagnetism with a sensitive atomicmagnetometer

E. Corsini1, N. Baddour1, J.M. Higbie2, B. Lester3, P. Licht4, B. Patton1, M. Prouty5,D. Budker1,6

1Department of Physics, University of California, Berkeley, CA 94720-73002Department of Physics, Bucknell University, Lewisburg, PA 17837

3Department of Physics, California Institute of Technology, Pasadena, CA 911254UC Botanical Garden, University of California, Berkeley, CA 94720

5Geometrics, 2190 Fortune Drive, San Jose, CA 951316Nuclear Science Div., Lawrence Berkeley National Laboratory, Berkeley CA 94720

The detection of biological magnetic signals has added a new dimension to the under-standing of physiological and biological processes1 . Superconducting quantum inter-ference device (SQUID) magnetometers have been leading the field of ultra-sensitivemagnetic field measurements2 ; however the area of resonant magneto-optics and atomicmagnetometry has experienced a resurgence driven in particular by new techniques inproducing dense atomic vapors with long-lived polarized ground-states. Atomic magne-tometers have now achievied sensitivities surpassing that of SQUIDs3 and, in contrast toSQUIDs which measure magnetic flux and require cryogenics, atomic magnetometersoperate at room temperature and measure the absolute magnetic field.

Plant bio-processes span several minutes to several hours and the expected magneticfield from such processes is small. We select the Titan arum (Amorphophallus titanum)inflorescence known for its fast bio-chemical processes while blooming and we reportwhat we believe is the first (null) measurement of plant bio-magnetism with a sensitiveatomic magnetometer (Geometrics G858). We show that the upper bound for the surfacemagnetic field from these processes is less then ∼0.6 µG. Prospects for more sensitivemeasurements will be presented.

The titan arum (Amorphophallus titanum), nicknamed‘Trudy’, in full bloom on June 23, 2009, at the University ofCalifornia Botanical Garden. The Geometrics G858 atomicmagnetometer sensors are positioned behind the plant.

1G. G. Matthews,“Cellular Physiology of Nerve and Muscle”, Wiley-Blackwell, 4th ed. (2002)2J. Clarke, A. Braginski,“The SQUID Handbook”, Vol. I & II, Wiley (2004)3D. Budker, M. Romalis, Nature Physics 3, 227 (2007)Sponsors: ONR, MURI, U.S. Dept. of Energy (LBNL Nuc. Sc. Div. Contr. DE-AC03-76SF00098).

Spectroscopy Th 142 551

Transformation from EIA into EIT by incoherentpumping in 85Rb D1 line

J.D. Kim1, H. Yu1, K.D. Jang1 J.B. Kim1

1Department of Physics Education, Korea National University of Education,Chung-Buk, 363-791, Korea

In open systems of 85Rb D1 line, we have observed electromagnetically induced absorp-tion(EIA) using two coherent laser fields 1. Transformation from EIA into electomag-netically induced transparency(EIT) by adding a pump laser beam, which is incoherentwith coupling beam, is occurred as Figure 1. Absorption spectra were observed depend-ing on intensities and polarizations of each laser beams and transition lines. However,in a closed system of 87Rb D2 line, this transformation was not found in Figure 2. Wereport an experimental observation of such transformation in an Rb vapor cell.

Figure 1: Absorption spectra of the transition F=3→F’=2,3 in the open system of85Rb D1 line. Transformation is happened by adding pump laser.

Figure 2: Absorption spectra of the transition F=3→F’=3,4 in the closed system of87Rb D2 line. EIA is not changed to EIT when adding the pump laser.

1S. K. kim, H. S. Moon, K. D. Kim, and J. B. Kim,”Observation of electromagnetically induced absorptionin open system regardless of angular momentum” Phys. Rev. A 68. 063813 (2003).


Isotope shifts and hyperfine structure of the Fe I373.7 nm resonance line

S. Krins, N. Huet, T. Bastin

Institut de Physique Nucleaire, Atomique et de Spectroscopie, Universite de Liege,Belgium

We report the observation of ultrahigh resolution spectra of resonance lines in Ironatoms. The spectra have been recorded using the saturated absorption laser spectroscopytechnique combined with lock-in amplification of the signals. The experimental arrange-ment is illustrated in Fig. 1. The resolution λ/∆λ of the reported lines is of the order60 millions and allows a neat observation of the optical isotope shifts of the transition3d64s2 5D3 → 3d64s4p 5F o

4 at 373.7 nm for the 4 natural iron isotopes 54Fe, 56Fe, 57Feand 58Fe. All those shifts have been measured using frequency markers generated with aFabry-Perot interferometer. Among the 4 natural isotopes, 57Fe is the only one to have anuclear spin and to present consequently an hyperfine structure. This hyperfine structurehas been measured using enriched samples of this particular isotope. First results aboutthe hyperfine constant A of the upper level 3d64s4p 5F o

4 will be presented. The authorsthank the belgian F.R.S.-FNRS for financial support.

Figure 1: Experimental arrangement used for the observation of Doppler-freesaturated absorption spectra of the 373.7 nm resonance line in neutral iron.


Zero-field nuclear magnetic resonance withparahydrogen induced polarization

M.P. Ledbetter1, G. Kervern2, P. Ganssle2, T. Theis2 A. Pines2,3 D. Budker2,4

1Department of Physics, University of California at Berkeley, Berkeley, CA 947202Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720

3Materials Science Division, Lawrence Berkeley Laboratory, Berkeley CA 947204Nuclear Science Division, Lawrence Berkeley Laboratory, Berkeley CA 94720

Nuclear magnetic resonance (NMR) is a powerful analytical tool for elucidating molec-ular structure and function. Conventionally, NMR is detected using inductive pickupcoils in large magnetic fields, necessitating expensive and immobile superconductingmagnets. The development of sensitive low-frequency magnetic field detectors suchas superconducting quantum interference devices or atomic magnetometers reduces theneed for such superconducting magnets, and has sparked considerable interest in NMRand magnetic resonance imaging in low values of the magnetic field.

One of the key parameters extracted from NMR spectra to determine molecularstructure are scalar spin-spin couplings (an interaction of the form JI1 · I2). Recently,we have demonstrated that such couplings can be detected in zero-magnetic field us-ing microfabricated atomic magnetometers1 using permanent magnets to pre-polarize asample. In addition to eliminating superconducting magnets, the benefits of working inzero magnetic field include extremely high field homogeneity, both spatially and tempo-rally, allowing narrow lines (we have demonstrated 100 mHz lines without employingspin-echoes) and very accurate determination of coupling parameters.

More recently we have demonstrated that parahydrogen, the singlet state of H2, canbe used to produce observable magnetization at zero magnetic field without the use ofany prepolarizing magnet. Figure 1 shows the zero field J-spectra of natural abundanceethylbenzene polarized via hydrogenation of styrene with pH2. For comparison, theexpected signal from ethylbenzene prepolarized in a 2 T magnetic field would be belowthe noise level. New results on zero field decoupling sequences and multi-dimensionalspectroscopy will also be presented.

0 50 100 150 200 250 300

0.0000

0.0001

0.0002

0.0003

0.0004

Frequency HHzL

Mag

nitu

deSi

gnalHVL

Figure 1: Zero field J-spectra of ethylbenzene, polarized via parahydrogen.

1M.P. Ledbetter, C.W. Crawford, A. Pines, D.E. Wemmer, S. Knappe, J. Kitching, D. Budker, “OpticalDetection of NMR J-Spectra at Zero Magnetic Field”, Journal of Magnetic Resonance 199, 25-29 (2009).


Precision spectroscopy of atomic helium 21S0 - 21P1

transitionP.L. Luo1, J.T. Shy1,2,

1Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

The laboratory experiments of helium are important due to helium is the simplesttwo-electron neutral atom and it is one of the major elements in the Universe. Besides,the measurements of absolute frequencies and the isotope shifts of atomic helium tran-sitions are useful tests of the theoretical calculations1.

We have started a research project on the precision spectroscopy of 21S0 - 21P1

transition of atomic helium using a 2 µm single-frequency tunable laser. This laser is adiode-pumped Tm,Ho:YLF laser. A VBG (volume Bragg grating) is used as the wave-length tuning element and the output coupler of the laser cavity as well. The 21S0 - 21P1

transitions of 3He and 4He will be studied by the saturation absorption spectroscopy andtheir absolute frequencies will be measured using an optical frequency comb. In the endthe isotope shift and hyperfine structure of 3He will be determined accurately.

In this poster, we will present the schemes of 2 µm single-frequency tunable laser,Doppler-free saturated absorption spectroscopy of 21S0 - 21P1 transition in atomic Heand the optical frequency comb. We will also discuss how to analyze the hyperfine levels21P1,1/2 and 21P1,3/2 of 3He, as shown on Figure 1.

0

16000

16500

17000

17500

18000

Ene

rgy

Leve

ls (c

m-1)

21P1

21S0

11S0

21P1 F=3/2

21P1 F=1/2

20.78 MHz2058 nm

RF discharge

Figure 1: Energy levels of 21S0 - 21P1 transition of 3He

1D. C. Morton, Qixue Wu, and G. W. F. Drake, “ Energy levels for the stable isotopes of atomic helium(4He I and 3He I).”, Can. J. Phys. 84, 83-105 (2006).


Observation of a Frequency-Shift in a Rb AbsorptionSpectrum using an Optical Nanofibre in a Vapour Cell

A. Watkins1,2, K. Deasy2,3, J. Ward2 S. Nic Chormaic1,2

1Physics Department, University College Cork, Cork, Ireland2Photonics Centre, Tyndall National Institute, Prospect Row, Cork, Ireland

3Department of Applied Physics and Instrumentation, Cork Institute of Technology,Cork, Ireland

In recent years, tapered optical fibres with subwavelength diameters, fabricated usinga direct-heating technique1, have attracted considerable research attention as tools fortrapping and manipulating neutral atoms. Previously, we have shown that they are idealtools for probing magneto-optical trap characteristics by coupling photons from a laser-cooled cloud of rubidium atoms into the guided mode of a nanofibre.2 Conversely,atoms can absorb photons from the guided mode via an evanescent field when light of awavelength comparable to the waist diameter of the nanofibre propagates through it.

In this work, we present recent experimental results whereby surface interactions ofa rubidium vapour with a nanofibre were investigated. The frequency of a transmittedprobe beam is scanned over a reference spectrum as a vapour is added to the cell. A red-shift of ∼50 MHz, due to van der Waals interactions, is clearly dominant in the nanofibrespectrum with respect to the reference signal which was recorded simultaneously (Fig.1). Future work will involve incorporating a whispering gallery mode resonator into thesetup, via coupling with the nanofibre, to further enhance the sensitivity of the systemfor bio-sensing applications.

2 4 6 8 10 120.8

1.2

1.6

2.0

87Rb F=1

85Rb F=285Rb

F=3

87Rb F=2SA

S si

gnal

(V)

Frequency (GHz)

SAS Ref. Signal Nanofibre 6A

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

Nanofibre signal (V)

Figure 1: Absorption signal through an optical nanofibre, transmission ∼2%, for the D2lines in 85Rb and 87Rb with respect to a reference saturated absorption signal.

1J.M. Ward, D.G. O’Shea, B.J. Shortt, M.J. Morrissey, K. Deasy and S. Nic Chormaic, Rev. Sci. Instrum.77, 083105 (2006).

2M. Morrissey, K. Deasy, Y. Wu, S. Chakrabarti and S. Nic Chormaic, Rev. Sci. Instrum. 80, 053102(2009).


Separating krypton tracers from air samples for ultrasensitive collinear fast beam laser spectroscopy

T. Mohamed1, R. Nava2, M. Fahes1, H. Nasrabadi1, K. Okada3, M Wada4,H.A. Schuessler1,2

1Science Department, Texas AM University at Qatar, Doha 23874, Qatar2Texas AM University College Station, TX 77843, USA

3Department of Physics, Sophia University, 7-1 Chiyoda, Tokyo 102-8554, Japan4Atomic Physics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

85Kr is a long lived radio-isotope (T1/2=10.7 years) which is being used as a tracerin gas and oil reservoirs, since it does not occur naturally. We describe our laser spec-troscopy apparatus together with a method for isolating the tracers in the samples andmeasure krypton isotope ratios.

We developed a portable apparatus for collecting, separating, and enriching of kryp-ton from environmental air samples. The device is mainly based on cryogenic trappingof the gases at liquid nitrogen temperature on traps. In particular, the apparatus consistsof a molecular sieve trap for the elimination of H20 and CO2, charcoal traps for thecollection of krypton and other gases and three stages of gas chromatography to achieveseparation and purification of krypton from mainly N2, O2, and Ar. Spurious residualN2 and other reactive gases still remaining after the third stage of chromatography areremoved at the final stage on a hot Ti sponge getter. A thermal conductivity detector isused to monitor the characteristic elution time of the various components of condensedgases in the traps after warming the traps from liquid nitrogen gradually to boiling watertemperatures. This allows optimizing the switching time of the valves between the threestages of gas chromatography in such way that mainly krypton is selected and loadedto the next stages while removing the other gases to the exhaust using He gas for trans-portation. The krypton separation efficiency is determined using a residual gas analyzerand will be given for a variety of samples.

This research is supported by the Qatar Foundation under the NPRP grant 30-6-7-351

1R. Nava, H. Schuessler, M. Fahes, H. Nasrabadi, and A. Kolomenski, SPE Annual Technical Confer-ence and Exhibition, 4-7 October 2009, New Orleans, Louisiana, SPE 124689.


High selectivity and sensitivity time of flight massspectroscopy of Xenon tracers

J. Strohaber1, T. Mohamed2, R. Nava1, M. Fahes2, H. Nasrabadi2, K. Okada3,M. Wada4, H.A. Schuessler1,2

1Texas AM University College Station, TX 77843, USA2Science Department, Texas AM University at Qatar, Doha 23874, Qatar

3Department of Physics, Sophia University, 7-1 Chiyoda, Tokyo 102-8554, Japan4SLOWRI Team, Nishina Accelerator Center, RIKEN, Japan

A reflectron type time-of-fight ion mass spectrometer has been developed to measurexenon isotope ratios. In this work, Xe ions were produced by irradiating target neu-tral atoms with radiation from a near terawatt (∼ 1012 ) laser system having a centralwavelength of 800 nm, a pulse duration of ∼ 45 fs , and a repetition rate of 1 kHz. Aset of parallel plates accelerated the ions into a flight tube where they were reflectedonto an MCP detector. This unique reflectron allows not only for the high precision (m∆m > 1000 for Xe+ and its isotopes) needed for efficient isotope measurements butalso for obtaining intensity-resolved spectra. Our initial results for the nine stable iso-topes of Xeq+ (q=1,2,3,4 ) are depicted below. By using a micrometer-sized slit andby carefully detuning our ion mirror, a one-to-one mapping between space and time-of-flight can be achieved allowing for the collection of ions from a region of space havingnearly constant laser intensity [1]. As shown below (inset), the central dip in the isotopesof the lower charge state Xe+ indicates the presence of higher-order processes such asthe production of multiply charged ions, which is consistent with a sequential ionizationpicture. We plan to process air samples and analyze them for radioactive 133Xe and135Xe tracers produced by neutron irradiation of fissionable materials within a nuclearreactor. For improved ion detection, future work will involve cryogenic xenon enriching,the use of a pulsed gas valve, and a multi kilohertz laser system.

This work was partially supported by the Robert A. Welch Foundation (grant No.A1546), the National Science Foundation (grants Nos. 0722800 and 0555568), the AirForce Office of Scientific Research (grant FA9550-07-1-0069) and Qatar National Re-search Fund (grant NPRP30-6-7-35).

1.1J. Strohaber and C. J. G. J. Uiterwaal, Phys. Rev. Lett. 100, 023002 (2008).


Modulation transfer spectroscopy for accurate andwideband laser locking

V. Negnevitsky1,2, L. Kleeman2 and L. D. Turner1

1School of Physics and 2Department of Electrical and Computer Systems Engineering,Monash University, Victoria 3800, Australia

Diode laser locking systems are ubiquitous in atomic physics laboratories. Modulationtransfer spectroscopy (MTS) is a well-understood scheme for generating a laser fre-quency error signal from an atomic vapour reference. MTS offers wideband, drift-freelocking with no Doppler background, and an unambiguous lock to the closed transi-tions needed for atomic state manipulation. Despite this, MTS is seldom used in atomicphysics laboratories, perhaps because previous designs required resonant electro-opticmodulation. We present a novel spectrometer layout using inexpensive acousto-opticmodulators (AOMs) which allows for control bandwidths in excess of 1 MHz.

In modulation transfer spectroscopy, four-wave mixing occurs in an atomic vapourbetween sidebands of a frequency modulated pump laser and the probe laser. The result-ing amplitude modulation of the probe is demodulated to give a dispersive error signal.The four-wave mixing process is efficient only on closed transitions, providing a dis-tinctively simple locking spectrum (Fig. 1).

We show that a conventional AOM-based optical layout widely used for laser lockingcan be repurposed for MTS locking simply by redesigning the electronics. Modulationfrequencies of at least 3 MHz are achieved with standard AOMs. We describe the effectsof modulation frequency, demodulation phase and beam intensities on the slope, ampli-tude and recapture range of the MTS error signal. We also present progress towards anall-digital MTS lock controller using a field-programmable gate array.1

−1600 −1400 −1200 −1000 −800 −600 −400 −200 0

−4

−2

0

2

4

Detuning (MHz)

MT

S s

ign

al (V

)

0.3

0.35

0.4

0.45

0.5

SA

sig

na

l (V

)

a)

b)

Figure 1: Spectra of the rubidium D2 transitions using a) saturated absorption spectroscopy andb) MTS. The MTS spectrum is Doppler-free and provides lock points only for the closed transitions.

1Details at http://bec.physics.monash.edu.au/ModulationTransferLaserLock


Analysis of keV x-ray spectrum in laser-producedSamarium plasmas

J.Y. Zhong1, G Zhao1, J Zhang2,

1Key Laboratory of Optical Astronomy, National Astronomical Observatories, ChineseAcademy of Sciences, Beijing 100012, China

2Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences,Beijing 100080, China

We have studied the characteristics of x-ray emissions in the 6.5-10A range from theplasmas produced by the irradiation of samarium slab targets with a laser pulse of 600ps duration at an intensity of 4×1013W cm−2. The prominent lines of Ni-, Co-, Fe-, andMn-like Sm ions arising from 4f-3d radiative transition are identified. The analysis of thekeV spectra indicates that the plasmas depart from pure local thermal equilibrium (LTE)regime. A collisional-radiative model has been constructed to simulate this spectrum.The intensity ratio of the resolved Ni-like Sm lines is shown to be a useful tool forelectron density diagnosis.1, 2

Figure 1: Modification of the calculated Sm spectrum by multiplying the Co-, Fe-and Mn-like lines by factors of 0.269, 0.034 and 0.005 separately to fit the experimentalratio of the 4f-3d transitions from different ionization stages. Labels by alphabet corre-spond to the transition identification in Table 1. Dashed lines are experimental resultsand solid lines are theoretical results.

1Electronic address: [email protected] author gratefully acknowledges the support of K. C. Wong Education Foundation, Hong Kong

560 Th 151 Tests of Fundamental Physics...

A femtosecond frequency comb for application in a dualspecies atom interferometer to test the Universality of

Free Fall.A. Resch, S. Herrmann for the QUANTUS team

ZARM - Center of Applied Space Technology and Microgravity, Universitat Bremen,Am Fallturm 1, 28359 Bremen

We use a compact fiber-based femtosecond frequency comb in the zero-gravity en-vironment of the Bremen drop tower to evaluate concepts for its application in a freelyfalling dual species atom interferometer aiming to test the Universality of Free Fall(UFF). A drop tower compatible apparatus which is currently prepared by the QUAN-TUS collaboration will provide an ultra-cold mixture of Rb and K atoms as the sourcefor such a dual species atom interferometer. The two interferometers shall be operatedas a differential accelerometer where the extended time of free fall accessible in thedrop tower (up to 9 s when operated in catapult mode) should allow for significantlyincreased resolution per shot. The frequency comb will then be used to provide a phase-link between the Raman lasers of the two atom interferometers at 780 nm and 767 nmrespectively, to enable a precision measurement of the differential phase and thus thedifferential acceleration. The frequency comb is based on a femtosecond fiber laser andwas designed by Menlo Systems specifically for the use in a drop tower experiment.Such an experiment in the drop tower is intended to serve as a pathfinder for a futurespace based implementation e.g. on the International Space Station, where the full po-tential of matter wave interferometry with extended free evolution time and integrationover a large number of measurements might be realized.We will present the underlying concepts for the application of the comb in a test of theUFF and report on the current status of the drop tower experiment.We acknowledge support by the German Space Agency DLR with funds provided bythe Federal Ministry of Economics and Technology (BMWi) under grant number DLR50 WM 0842.

Tests of Fundamental Physics... Th 152 561

Production of Ba meta-stable states via super-radianceN. Sasao1, A. Fukumi1, K. Nakajima1, I. Nakano1, H. Nanjo2, C. Ohae1, S. Sato1,

T. Taniguchi1, T. Yamaguchi1, M. Yoshimura1

1Okayama University, Okayama 700-8530, Japan2Kyoto University, Kyoto 606-8502, Japan

Recently some of the authors have found that coherent volume of super-radiance, aclass of cooperative coherent optical phenomenon predicted by Dicke in 1954 and con-firmed by subsequent experiments, 1 can be made free from its wavelength restrictionif a process under consideration emits plural particles or radiations.2 In fact, the coher-ent volume can be macroscopic when outgoing particles satisfy a certain phase matchingcondition. Our ultimate goal is use of this mechanism, named as ”macro-coherent ampli-fication mechanism”, for investigating natures of neutrinos, for example, their absolutemass scale, and mass type of Dirac or Majorana. 3

We present some preliminary results of an experiment which is intended to provethe principle of the macro-coherent amplification mechanism. We like to do it with aprocess which emits two photons from atomic states excited coherently (paired super-radiance): observation of back-to-back radiations with almost equal energy is an un-ambiguous proof of the principle. One important step of the experiment is to producemeta-stable states, the initial atomic states from which paired super-radiance is sup-posed to occur. The state we are of interests is Barium meta-stable states (6s5d, 1D2 );their radiative life time to the ground states (6s2,1S0 ) is ∼1/8 sec. We obtain them viasuper-radiance from intermediate states (6s6p, 1P1 ).

In the actual experiment, we injected 554nm laser lights to excite Ba atoms to 1P1 .One salient feature of our method was use of a trigger laser; 1500nm CW laser lightscorresponding to 1P1 −1D2 energy difference was injected to accelerate the transition.Fig.1 shows the results; the angular dependence of 1500nm super-radiance intensity ob-served by a photo-diode detector without (a) and with (b) the trigger laser. Introductionof trigger laser not only speeded up the transition from 1P1 to 1D2 but also sharpened itsangular divergence. We obtained the 1D2 production rate of 1013 atoms in a few nanoseconds. The results of the experiment will be reported in detail.

(b)(a)

x [mm] x [mm]y [mm] y [mm]

Figure 1: Angular distribution of super-radiance without (a) and with (b) trigger laser.

1R.H. Dicke, Phys. Rev. 93, 99 (1954), see also M. Benedict et.al., Super-radiance (Informa, 1996)2M.Yoshimura et.al., arXiv:0805.1970v1 [hep-ph] 14 May 20083M.Yoshimura, Phys. Rev. D 75, 113007 (2007); M.Yoshimura et.al., Prog. Theo. Phys. 123, 523 (2010)


Towards a Quantum Test of the Equivalence PrincipleUsing Atom Interferometry

D. Schlippert1,2, J. Hartwig1,2, U. Velte1,2, N. Winter1,2, M. Zaiser1,2, V. Lebedev1,2,W. Ertmer1,2 and E.M. Rasel1,2

1Institute of Quantum Optics, Leibniz Universitt Hannover, Welfengarten 1, 30167Hannover, Germany

2Centre for Quantum Engineering and Space-Time Research - QUEST, Cluster ofExcellence, Welfengarten 1, 30167 Hannover, Germany

We present our experimental approach to a dual species atom interferometer per-forming a differential acceleration measurement with quantum objects, namely 87Rband 39K atoms, to test the weak equivalence principle (Universality of Free Fall, UFF).

A compact and versatile laser system provides 5 W for incoherent and coherentmanipulation of both species allowing for trapping, cooling and driving stimulated Ra-man transitions with the same laser setup. Atoms are loaded into a three dimensionalmagneto-optical trap (3D-MOT) using a 2D-MOT. The system provides an optical dipoletrap at a wavelength of 1.96 µm to enable very accurate initial position control of thetwo ensembles and leaves options for evaporative and sympathetic cooling and the useof quantum degenerate gases in the differential interferometer. After dropping the atomsfrom the dipole trap a Mach-Zehnder interferometry sequence will be performed forboth species simultaneously . A detection cube below the trapping region allows forhigh NA state selective fluorescence detection.

Tests of Fundamental Physics... Th 154 563

Progress on the measurement of the francium anapolemoment

D. Sheng1, J. Hood1, S. Lynam1, J. Zhang1, L. A. Orozco1, FrPNC Collaboration.

1Joint Quantum Institute, Department of Physics, University of Maryland and NationalInstitute of Standards and Technology, College Park, MD, USA

We present the current status of the experimental effort towards the measurement of theanapole moment in francium. The anapole moment is a parity violating, time-reversalconserving nuclear moment that arises from the weak interaction among nucleons. Itis nuclear spin dependent (nsd) and sensitive to the configuration of nuclear structure.Our experimental scheme is to perform a direct measurement of the nsd parity viola-tion, by driving a parity forbidden E1 transition between hyperfine ground states in aseries of francium isotopes inside a blue detuned dipole trap at the electric anti-nodeof a microwave cavity. We explore on the possible tests using rubidium isotopes. Theprogress includes the design of a Fabry-Perot microwave cavity, the test of phase con-trolled interference between interactions and applications of the blue detuned dipole trapon the study of classical atom trajectories. The francium experiment will be at the ISACradioactive beam facility of TRIUMF, Canada. Work supported by NSF and DOE, USA.


Symmetry Consequences of Special Relativity in anExpanding Hyperbolic Cosmology

Felix T. Smith

SRI International, Menlo Park, CA, USA

Special relativity (SR) can be extended to the hyperbolic geometry of the simplestuseful model of the Hubble expanding universe. Both position and velocity space thenhave negative curvature and each separately supports its own Lorentz subgroup Lposnand Lvel. These combine in a direct product group, the double Lorentz group L2 =Lposn ⊗ Lvel. Cosmic time tcosm is orthogonal to the hyperbolic variables of both thevelocity and position spaces, and has its own one-parameter translational subgroup. Thiscombines with the 12-parameter group L2 to form the 13-parameter hyperbolic Poincaregroup Phyp. Position 3-space expands linearly in cosmic time tcosm. Translationalshifts are like boosts in velocity space, but expressed through an increment ∆r scaledby the Hubble radius ρ = ctcosm. The operators of the direct product group mustbe represented by 8x8 matrices, constructed block-diagonally from the 4x4 matrices ofthe subgroups Lposn and Lvel. The spatial curvature entails new angular momentumeffects, arising because each of the two Lorentz subgroups has its own R(3) rotationalsubgroup. These bring in new operators permitting very weak transitions that would betotally forbidden under the zero curvature symmetry of flat Minkowski space-time in thePoincare group. Because some of these operators appear only as 8x8 matrices, they canrepresent curvature effects in dynamics that will not appear at all at the level of the 4x4tensors of special and general relativity. A coupling operator appears that depends onthe product (r × v)/cρ. Since ρ, the Hubble length, is a measure of curvature length,this term is very weak and vanishes when the curvature vanishes. Its presence suggeststhere will be stronger effects of a similar kind in the presence of stronger local curvaturefeatures. Such terms will be expected to be important especially in regions of highcurvature arising from strong gravitation fields.

Trapped Ions Th 156 565

High-power picosecond laser source with 300 MHzrepetition rate for trapped-ion quantum logic

M.J. Petrasiunas1, M.G. Pullen1, J. Canning2, M. Stevenson2, P.S. Westbrook3,K.S. Feder3, D. Kielpinski1

1Centre for Quantum Dynamics, Griffith University, Nathan QLD 4111, Australia2Interdisciplinary Photonics Laboratories (iPL), School of Chemistry, Madsen

Building F09, University of Sydney, Sydney NSW 2006, Australia3OFS Laboratories, Somerset, New Jersey 08873, USA

Trapped ions are a major candidate technology for scalable quantum computation. How-ever, current methods for performing quantum logic gates with trapped ions are limitedby the trap frequency. A scheme has been developed where this limitation is removed,potentially allowing for a factor of 103 increase in gate speed.1 The scheme uses pairsof counterpropagating π-pulses, resonant with an allowed ion transition, which impart alarge selective force that scales with repetition rate of the laser source.

We are developing a fibre-based source of picosecond pulses resonant with the 370nm allowed transition of the Yb+ ion. We first produce mode-locked 1108 nm light froman octave-spanning supercontinuum with fibre Bragg grating (FBG) enhancement at thedesired wavelength.2 We filter this wavelength and reamplify to 10 W of average power,which will undergo second harmonic generation (SHG). The produced 555 nm lightundergoes sum frequency generation (SFG) with the remaining IR. We present worktoward efficient upconversion, where simulations show a 25% upconversion efficiencyof this light to 370 nm for these parameters.

We use an Er-doped fibre laser, harmonically mode-locked at a 300 MHz repetitionrate, to seed the supercontinuum generation — this directly determines the output rep-etition rate. This technique is scalable to very high average power and repetition rate,allowing for good resonant gate performance in highly parallel logic operations.3

1J.J. Garcia-Ripoll, P. Zoller, and J.I. Cirac, ”‘Speed Optimized Two-Qubit Gates with Laser CoherentControl Techniques for Ion Trap Quantum Computing,” Phys. Rev. Lett. 91, 157901 (2003)

2D. Kielpinski et al., ”Mode-locked picosecond pulse generation from an octave-spanning supercontin-uum,” Opt. Express 17, 20833-20839 (2009)

3D. Hayes et al., ”Entanglement of Atomic Qubits Using an Optical Frequency Comb,” Phys. Rev. Lett.104, 140501 (2010)

566 Th 157 Trapped Ions

Spin Dependent Forces on Trapped Ions: EntangledMatter Wave Dynamics and Decoherence

U.G. Poschinger1,2, A. Walther1,2, F. Ziesel1,2, M. Hettrich1,2, K. Singer1,2,F. Schmidt-Kaler1,2

1Institut fur Quantenphysik, Universitat Mainz, Staudingerweg 7, 55128 Mainz,Germany

2Institut fur Quanteninformationsverarbeitung, Universitat Ulm, Albert-Einstein-Allee11, 89081 Ulm, Germany

We aim at the experimental realization of scalable quantum information with qubits en-coded in the electron spin of 40Ca+ ions in a segmented microchip ion trap. The qubitmanipulation for single- and two qubit gates are realized by stimulated Raman transi-tions driven by off-resonant laser fields [1]. We present a detailed study of the quantumdynamics of a single trapped ion exposed to laser fields which resonantly drive its mo-tion along the trap axis. The precise investigation of the ions dynamics is a fundamentalimportance for the realization of fast and accurate two-ion gates, and a cornerstone forthe application of advanced quantum control techniques. We show complementary ap-proaches for the readout of the motional state: i) by monitoring the ions spin coherence,ii) by reconstructing the quantum state of the motional degree of freedom by mappingout phonon number distribution and iii) by measuring the ions trajectory in phase spacewith a wavepacket homodyne measurement. We show that with the latter method, a si-multaneous statistical measurement of position and momentum with an accuracy belowthe Heisenberg limit is possible. As a result, we measure deviations from the dynam-ics predicted by the Lamb-Dicke approximation [2]. Furthermore, we present a detailedstudy of the relevant decoherence processes. These include on the one hand spontaneousphoton scattering, for which we have measured the effect of the scattering of the mo-tional state of the ion. On the other hand, we have investigated the effect of the initialion temperature on the dynamics of spin and motion, allowing precise estimates of therequirements for scalable quantum information in microstructured ion traps.[1] U. G. Poschinger et al., J. Phys. B: At. Mol. Opt. Phys. 42 154013[2] U. G. Poschinger et al., in preparation

Trapped Ions Th 158 567

Generation of entangled states of two ions usingadiabatic passage

K. Toyoda, S. Nomura, T. Kimura, T. Watanabe, S. Haze, S. Urabe

Graduate school of Engineering Science, Osaka University, Japan

Multipartite entanglement plays a central role in quantum information science. Invarious systems, including photons and trapped ions, entangled states are generated andstudied, while with increased numbers of particles it becomes difficult to generate andanalyze such states.

For a string of ions, a relatively simple and effective method for generation of animportant class of entangled states called symmetric Dicke states is proposed by Lining-ton et al.[1], which requires at minimum only two chirped pulses for adiabatic passage.Symmetric Dicke states are defined as |D(m)

N ⟩ ≡ (NCm)−1/2∑

k Pk(| ↓⊗(N−m)↑⊗m⟩)(the sum is over all NCm permutations denoted as Pk), which is known to be robustagainst partial measurement or loss of particles. The method in [1] is applicable to|D(m)

N ⟩ with arbitrary N and m. For smaller numbers of excitation m, non-chirpedpulses can also be used to produce |D(m)

N ⟩, although in this case perfect fidelity is pos-sible only when m = 1. Hume et al. [2] analyzed attainable fidelities with the methodusing non-chirped pulses and experimentally demonstrated it using two 25Mg+ ions.Sufficiently high fidelities are estimated in [2] for m = 2, 3 with non-chirped pulses,while use of adiabatic passage may make the generation process insensitive to such im-perfections as intensity fluctuation or frequency drift of lasers.

We have generated an entangled state of two ions, |D(1)2 ⟩, by using adiabatic passage

on the S1/2–D5/2 transition of 40Ca+. Fig. 1 shows a parity oscillation with frequency 2when additional two π/2 analysis pulses are applied with the phase of the second varied.From this and population measurements, we infer that |D(1)

2 ⟩ is generated with fidelityexceeding 0.6. Details including fidelity analysis will be given in the session.

[1]I. E. Linington and N. V. Vitanov, Phys. Rev. A 77, 010302 (2008).[2]D. B. Hume, C. W. Chou, T. Rosenband and D. J. Wineland, Phys. Rev. A 80, 052302 (2009).

0 0.2 0.4 0.6 0.8-1

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-0.4

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0

0.2

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0.6

0.8

1

Phase/2π

Parity

sin fit

Figure 1: Parity oscillation after two π/2 analysis pulses.

568 Th 159 Trapped Ions

Superconducting microfabricated ion traps for studies ofanomalous heating in trapped ions

S. X. Wang1, J. Labaziewicz1, Y. Ge1, E. Dauler2, K. Berggren2, I. L. Chuang1

1Center for Ultracold Atoms, Massachusetts Institute of Technology, Cambridge, USA2Research Laboratory of Electronics, Massachusetts Institute of Technology,

Cambridge, USA

Dense arrays of ions in microfabricated traps are a promising possibility for scaling upion trap quantum information processing. However, heating rates far exceeding Johnsonnoise limits severely affects the motional state coherence at small trap sizes. Currentevidence shows that by cooling to cryogenic temperatures, the anomalous heating isreduced by orders of magnitude from room temperature values, though still above thethermal limit12. This invites the possibility of distinguishing candidate noise models bycomparing traps made of normal metals and of superconductors. For example, chargenoise from bulk sources should be suppressed in superconducting traps. We fabricatesuperconducting ion traps with niobium and niobium nitride and trapped single 88Srions at cryogenic temperatures. The lowest observed heating rate is comparable to thatin gold and silver traps, suggesting that anomalous heating is primarily caused by sur-face, not bulk, effects. Heating rates above and below the superconducting transition arecompared to further investigate the effect of charge fluctuations on ion heating. Nev-ertheless, we show that anomalous heating need not be a limiting factor in gate fidelityand that microfabricated traps are compatible with quantum operations, by performinga controlled-NOT gate using a single ion’s atomic and motional states3. This demon-stration of superconducting ion traps opens up possibilities for integrating trapped ionsand molecular ions with superconducting devices, such as photon counting detectors,microwave resonators, and circuit-QED systems4.

1J. Labaziewicz et al., Phys. Rev. Lett. 100, 013001 (2008)2J. Labaziewicz et al., Phys. Rev. Lett. 101, 180602 (2008)3S. X. Wang et al., arxiv:0912.48924D. I. Schuster et al., arxiv:0903.3552

single ion imaging with a microfabricated optic · one real-world application of atomic vapour...

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